diff --git a/.npmignore b/.npmignore
index 1ca47212f..541f88d68 100644
--- a/.npmignore
+++ b/.npmignore
@@ -2,3 +2,4 @@ node_modules
 coverage
 examples
 tests
+*.test.js
diff --git a/lib/packExternalModules.js b/lib/packExternalModules.js
index c9b33564e..ee71b8974 100644
--- a/lib/packExternalModules.js
+++ b/lib/packExternalModules.js
@@ -3,10 +3,11 @@
 const BbPromise = require('bluebird');
 const _ = require('lodash');
 const path = require('path');
-const childProcess = require('child_process');
 const fse = require('fs-extra');
 const isBuiltinModule = require('is-builtin-module');
 
+const Packagers = require('./packagers');
+
 function rebaseFileReferences(pathToPackageRoot, moduleVersion) {
   if (/^file:[^/]{2}/.test(moduleVersion)) {
     const filePath = _.replace(moduleVersion, /^file:/, '');
@@ -16,18 +17,6 @@ function rebaseFileReferences(pathToPackageRoot, moduleVersion) {
   return moduleVersion;
 }
 
-function rebasePackageLock(pathToPackageRoot, module) {
-  if (module.version) {
-    module.version = rebaseFileReferences(pathToPackageRoot, module.version);
-  }
-
-  if (module.dependencies) {
-    _.forIn(module.dependencies, moduleDependency => {
-      rebasePackageLock(pathToPackageRoot, moduleDependency);
-    });
-  }
-}
-
 /**
  * Add the given modules to a package json's dependencies.
  */
@@ -200,156 +189,121 @@ module.exports = {
     const packagePath = includes.packagePath || './package.json';
     const packageJsonPath = path.join(process.cwd(), packagePath);
 
-    this.options.verbose && this.serverless.cli.log(`Fetch dependency graph from ${packageJsonPath}`);
-    // Get first level dependency graph
-    const command = 'npm ls -prod -json -depth=1';  // Only prod dependencies
-
-    const ignoredNpmErrors = [
-      { npmError: 'extraneous', log: false },
-      { npmError: 'missing', log: false },
-      { npmError: 'peer dep missing', log: true },
-    ];
-
-    return BbPromise.fromCallback(cb => {
-      childProcess.exec(command, {
-        cwd: path.dirname(packageJsonPath),
-        maxBuffer: this.serverless.service.custom.packExternalModulesMaxBuffer || 200 * 1024,
-        encoding: 'utf8'
-      }, (err, stdout, stderr) => {
-        if (err) {
-          // Only exit with an error if we have critical npm errors for 2nd level inside
-          const errors = _.split(stderr, '\n');
-          const failed = _.reduce(errors, (failed, error) => {
-            if (failed) {
-              return true;
-            }
-            return !_.isEmpty(error) && !_.some(ignoredNpmErrors, ignoredError => _.startsWith(error, `npm ERR! ${ignoredError.npmError}`));
-          }, false);
-
-          if (failed) {
-            return cb(err);
-          }
-        }
-        return cb(null, stdout);
-      });
-    })
-    .then(depJson => BbPromise.try(() => JSON.parse(depJson)))
-    .then(dependencyGraph => {
-      const problems = _.get(dependencyGraph, 'problems', []);
-      if (this.options.verbose && !_.isEmpty(problems)) {
-        this.serverless.cli.log(`Ignoring ${_.size(problems)} NPM errors:`);
-        _.forEach(problems, problem => {
-          this.serverless.cli.log(`=> ${problem}`);
-        });
-      }
-
-      // (1) Generate dependency composition
-      const compositeModules = _.uniq(_.flatMap(stats.stats, compileStats => {
-        const externalModules = _.concat(
-          getExternalModules.call(this, compileStats),
-          _.map(packageForceIncludes, whitelistedPackage => ({ external: whitelistedPackage }))
-        );
-        return getProdModules.call(this, externalModules, packagePath, dependencyGraph);
-      }));
-      removeExcludedModules.call(this, compositeModules, packageForceExcludes, true);
-
-      if (_.isEmpty(compositeModules)) {
-        // The compiled code does not reference any external modules at all
-        this.serverless.cli.log('No external modules needed');
-        return BbPromise.resolve();
-      }
-
-      // (1.a) Install all needed modules
-      const compositeModulePath = path.join(this.webpackOutputPath, 'dependencies');
-      const compositePackageJson = path.join(compositeModulePath, 'package.json');
-
-      // (1.a.1) Create a package.json
-      const compositePackage = {
-        name: this.serverless.service.service,
-        version: '1.0.0',
-        description: `Packaged externals for ${this.serverless.service.service}`,
-        private: true
-      };
-      const relPath = path.relative(compositeModulePath, path.dirname(packageJsonPath));
-      addModulesToPackageJson(compositeModules, compositePackage, relPath);
-      this.serverless.utils.writeFileSync(compositePackageJson, JSON.stringify(compositePackage, null, 2));
-
-      // (1.a.2) Copy package-lock.json if it exists, to prevent unwanted upgrades
-      const packageLockPath = path.join(path.dirname(packageJsonPath), 'package-lock.json');
-      return BbPromise.fromCallback(cb => fse.pathExists(packageLockPath, cb))
-      .then(exists => {
-        if (exists) {
-          this.serverless.cli.log('Package lock found - Using locked versions');
-          try {
-            const packageLockJson = this.serverless.utils.readFileSync(packageLockPath);
-            /**
-             * We should not be modifying 'package-lock.json'
-             * because this file should be treat as internal to npm.
-             * 
-             * Rebase package-lock is a temporary workaround and must be
-             * removed as soon as https://github.com/npm/npm/issues/19183 gets fixed.
-             */
-            rebasePackageLock(relPath, packageLockJson);
-
-            this.serverless.utils.writeFileSync(path.join(compositeModulePath, 'package-lock.json'), JSON.stringify(packageLockJson, null, 2));
-          } catch(err) {
-            this.serverless.cli.log(`Warning: Could not read lock file: ${err.message}`);
-          }
+    // Determine and create packager
+    return BbPromise.try(() => Packagers.get.call(this, 'npm'))
+    .then(packager => {
+      // Get first level dependency graph
+      this.options.verbose && this.serverless.cli.log(`Fetch dependency graph from ${packageJsonPath}`);
+      const maxExecBufferSize = this.serverless.service.custom.packExternalModulesMaxBuffer || 200 * 1024;
+
+      return packager.getProdDependencies(path.dirname(packageJsonPath), 1, maxExecBufferSize)
+      .then(dependencyGraph => {
+        const problems = _.get(dependencyGraph, 'problems', []);
+        if (this.options.verbose && !_.isEmpty(problems)) {
+          this.serverless.cli.log(`Ignoring ${_.size(problems)} NPM errors:`);
+          _.forEach(problems, problem => {
+            this.serverless.cli.log(`=> ${problem}`);
+          });
         }
-        return BbPromise.resolve();
-      })
-      .then(() => {
-        const start = _.now();
-        this.serverless.cli.log('Packing external modules: ' + compositeModules.join(', '));
-        return BbPromise.fromCallback(cb => {
-          childProcess.exec('npm install', {
-            cwd: compositeModulePath,
-            maxBuffer: this.serverless.service.custom.packExternalModulesMaxBuffer || 200 * 1024,
-            encoding: 'utf8'
-          }, cb);
-        })
-        .then(() => this.options.verbose && this.serverless.cli.log(`Package took [${_.now() - start} ms]`))
-        .return(stats.stats);
-      })
-      .mapSeries(compileStats => {
-        const modulePath = compileStats.compilation.compiler.outputPath;
-
-        // Create package.json
-        const modulePackageJson = path.join(modulePath, 'package.json');
-        const modulePackage = {
-          dependencies: {}
-        };
-        const prodModules = getProdModules.call(this,
-          _.concat(
+  
+        // (1) Generate dependency composition
+        const compositeModules = _.uniq(_.flatMap(stats.stats, compileStats => {
+          const externalModules = _.concat(
             getExternalModules.call(this, compileStats),
             _.map(packageForceIncludes, whitelistedPackage => ({ external: whitelistedPackage }))
-          ), packagePath, dependencyGraph);
-        removeExcludedModules.call(this, prodModules, packageForceExcludes);
-        const relPath = path.relative(modulePath, path.dirname(packageJsonPath));
-        addModulesToPackageJson(prodModules, modulePackage, relPath);
-        this.serverless.utils.writeFileSync(modulePackageJson, JSON.stringify(modulePackage, null, 2));
-
-        // GOOGLE: Copy modules only if not google-cloud-functions
-        //         GCF Auto installs the package json
-        if (_.get(this.serverless, 'service.provider.name') === 'google') {
+          );
+          return getProdModules.call(this, externalModules, packagePath, dependencyGraph);
+        }));
+        removeExcludedModules.call(this, compositeModules, packageForceExcludes, true);
+  
+        if (_.isEmpty(compositeModules)) {
+          // The compiled code does not reference any external modules at all
+          this.serverless.cli.log('No external modules needed');
           return BbPromise.resolve();
         }
-
-        const startCopy = _.now();
-        return BbPromise.fromCallback(callback => fse.copy(path.join(compositeModulePath, 'node_modules'), path.join(modulePath, 'node_modules'), callback))
-        .tap(() => this.options.verbose && this.serverless.cli.log(`Copy modules: ${modulePath} [${_.now() - startCopy} ms]`))
+  
+        // (1.a) Install all needed modules
+        const compositeModulePath = path.join(this.webpackOutputPath, 'dependencies');
+        const compositePackageJson = path.join(compositeModulePath, 'package.json');
+  
+        // (1.a.1) Create a package.json
+        const compositePackage = {
+          name: this.serverless.service.service,
+          version: '1.0.0',
+          description: `Packaged externals for ${this.serverless.service.service}`,
+          private: true
+        };
+        const relPath = path.relative(compositeModulePath, path.dirname(packageJsonPath));
+        addModulesToPackageJson(compositeModules, compositePackage, relPath);
+        this.serverless.utils.writeFileSync(compositePackageJson, JSON.stringify(compositePackage, null, 2));
+  
+        // (1.a.2) Copy package-lock.json if it exists, to prevent unwanted upgrades
+        const packageLockPath = path.join(path.dirname(packageJsonPath), packager.lockfileName);
+        return BbPromise.fromCallback(cb => fse.pathExists(packageLockPath, cb))
+        .then(exists => {
+          if (exists) {
+            this.serverless.cli.log('Package lock found - Using locked versions');
+            try {
+              const packageLockJson = this.serverless.utils.readFileSync(packageLockPath);
+              /**
+               * We should not be modifying 'package-lock.json'
+               * because this file should be treat as internal to npm.
+               * 
+               * Rebase package-lock is a temporary workaround and must be
+               * removed as soon as https://github.com/npm/npm/issues/19183 gets fixed.
+               */
+              packager.rebaseLockfile(relPath, packageLockJson);
+  
+              this.serverless.utils.writeFileSync(path.join(compositeModulePath, packager.lockfileName), JSON.stringify(packageLockJson, null, 2));
+            } catch(err) {
+              this.serverless.cli.log(`Warning: Could not read lock file: ${err.message}`);
+            }
+          }
+          return BbPromise.resolve();
+        })
         .then(() => {
-          // Prune extraneous packages - removes not needed ones
-          const startPrune = _.now();
-          return BbPromise.fromCallback(callback => {
-            childProcess.exec('npm prune', {
-              cwd: modulePath
-            }, callback);
-          })
-          .tap(() => this.options.verbose && this.serverless.cli.log(`Prune: ${modulePath} [${_.now() - startPrune} ms]`));
-        });
-      })
-      .return();
+          const start = _.now();
+          this.serverless.cli.log('Packing external modules: ' + compositeModules.join(', '));
+          return packager.install(compositeModulePath, maxExecBufferSize)
+          .then(() => this.options.verbose && this.serverless.cli.log(`Package took [${_.now() - start} ms]`))
+          .return(stats.stats);
+        })
+        .mapSeries(compileStats => {
+          const modulePath = compileStats.compilation.compiler.outputPath;
+  
+          // Create package.json
+          const modulePackageJson = path.join(modulePath, 'package.json');
+          const modulePackage = {
+            dependencies: {}
+          };
+          const prodModules = getProdModules.call(this,
+            _.concat(
+              getExternalModules.call(this, compileStats),
+              _.map(packageForceIncludes, whitelistedPackage => ({ external: whitelistedPackage }))
+            ), packagePath, dependencyGraph);
+          removeExcludedModules.call(this, prodModules, packageForceExcludes);
+          const relPath = path.relative(modulePath, path.dirname(packageJsonPath));
+          addModulesToPackageJson(prodModules, modulePackage, relPath);
+          this.serverless.utils.writeFileSync(modulePackageJson, JSON.stringify(modulePackage, null, 2));
+  
+          // GOOGLE: Copy modules only if not google-cloud-functions
+          //         GCF Auto installs the package json
+          if (_.get(this.serverless, 'service.provider.name') === 'google') {
+            return BbPromise.resolve();
+          }
+  
+          const startCopy = _.now();
+          return BbPromise.fromCallback(callback => fse.copy(path.join(compositeModulePath, 'node_modules'), path.join(modulePath, 'node_modules'), callback))
+          .tap(() => this.options.verbose && this.serverless.cli.log(`Copy modules: ${modulePath} [${_.now() - startCopy} ms]`))
+          .then(() => {
+            // Prune extraneous packages - removes not needed ones
+            const startPrune = _.now();
+            return packager.prune(modulePath, maxExecBufferSize)
+            .tap(() => this.options.verbose && this.serverless.cli.log(`Prune: ${modulePath} [${_.now() - startPrune} ms]`));
+          });
+        })
+        .return();
+      });
     });
   }
 };
diff --git a/lib/packagers/index.js b/lib/packagers/index.js
new file mode 100644
index 000000000..790782f44
--- /dev/null
+++ b/lib/packagers/index.js
@@ -0,0 +1,38 @@
+'use strict';
+/**
+ * Factory for supported packagers.
+ * 
+ * All packagers must implement the following interface:
+ * 
+ * interface Packager {
+ * 
+ * static get lockfileName(): string;
+ * static getProdDependencies(cwd: string, depth: number = 1, maxExecBufferSize = undefined): BbPromise<Object>;
+ * static rebaseLockfile(pathToPackageRoot: string, lockfile: Object): void;
+ * static install(cwd: string, maxExecBufferSize = undefined): BbPromise<void>;
+ * static prune(cwd: string): BbPromise<void>;
+ * 
+ * }
+ */
+
+const _ = require('lodash');
+const npm = require('./npm');
+
+const registeredPackagers = {
+  npm: npm
+};
+
+/**
+ * Factory method.
+ * @this ServerlessWebpack - Active plugin instance
+ * @param {string} packagerId - Well known packager id.
+ * @returns {BbPromise<Packager>} - Promised packager to allow packagers be created asynchronously.
+ */
+module.exports.get = function(packagerId) {
+  if (!_.has(registeredPackagers, packagerId)) {
+    const message = `Could not find packager '${packagerId}'`;
+    this.serverless.cli.log(`ERROR: ${message}`);
+    throw new this.serverless.classes.Error(message);
+  }
+  return registeredPackagers[packagerId];
+};
diff --git a/lib/packagers/index.test.js b/lib/packagers/index.test.js
new file mode 100644
index 000000000..988b37b14
--- /dev/null
+++ b/lib/packagers/index.test.js
@@ -0,0 +1,68 @@
+'use strict';
+/**
+ * Unit tests for packagers/index
+ */
+
+const _ = require('lodash');
+const chai = require('chai');
+const sinon = require('sinon');
+const mockery = require('mockery');
+const Serverless = require('serverless');
+
+chai.use(require('sinon-chai'));
+
+const expect = chai.expect;
+
+describe('packagers factory', () => {
+  let sandbox;
+  let serverless;
+  let npmMock;
+  let baseModule;
+  let module;
+
+  before(() => {
+    sandbox = sinon.sandbox.create();
+    npmMock = {
+      hello: 'I am NPM'
+    };
+    mockery.enable({ useCleanCache: true });
+    mockery.registerAllowables([ './index', 'lodash' ]);
+    mockery.registerMock('./npm', npmMock);
+    baseModule = require('./index');
+    Object.freeze(baseModule);
+  });
+
+  after(() => {
+    mockery.disable();
+    mockery.deregisterAll();
+  });
+
+  beforeEach(() => {
+    serverless = new Serverless();
+    serverless.cli = {
+      log: sandbox.stub(),
+      consoleLog: sandbox.stub()
+    };
+
+    module = _.assign({
+      serverless,
+      options: {
+        verbose: true
+      },
+    }, baseModule);
+  });
+
+  afterEach(() => {
+    sandbox.reset();
+    sandbox.restore();
+  });
+
+  it('should throw on unknown packagers', () => {
+    expect(() => module.get.call({ serverless }, 'unknown')).to.throw(/Could not find packager/);
+  });
+
+  it('should return npm packager', () => {
+    const npm = module.get.call(module, 'npm');
+    expect(npm).to.deep.equal(npmMock);
+  });
+});
diff --git a/lib/packagers/npm.js b/lib/packagers/npm.js
new file mode 100644
index 000000000..da5a7caab
--- /dev/null
+++ b/lib/packagers/npm.js
@@ -0,0 +1,95 @@
+'use strict';
+/**
+ * NPM packager.
+ */
+
+const _ = require('lodash');
+const BbPromise = require('bluebird');
+const childProcess = require('child_process');
+
+class NPM {
+  static get lockfileName() {  // eslint-disable-line lodash/prefer-constant
+    return 'package-lock.json';
+  }
+
+  static getProdDependencies(cwd, depth, maxExecBufferSize) {
+    // Get first level dependency graph
+    const command = `npm ls -prod -json -depth=${depth || 1}`;  // Only prod dependencies
+
+    const ignoredNpmErrors = [
+      { npmError: 'extraneous', log: false },
+      { npmError: 'missing', log: false },
+      { npmError: 'peer dep missing', log: true },
+    ];
+
+    return BbPromise.fromCallback(cb => {
+      childProcess.exec(command, {
+        cwd: cwd,
+        maxBuffer: maxExecBufferSize,
+        encoding: 'utf8'
+      }, (err, stdout, stderr) => {
+        if (err) {
+          // Only exit with an error if we have critical npm errors for 2nd level inside
+          const errors = _.split(stderr, '\n');
+          const failed = _.reduce(errors, (failed, error) => {
+            if (failed) {
+              return true;
+            }
+            return !_.isEmpty(error) && !_.some(ignoredNpmErrors, ignoredError => _.startsWith(error, `npm ERR! ${ignoredError.npmError}`));
+          }, false);
+
+          if (failed) {
+            return cb(err);
+          }
+        }
+        return cb(null, stdout);
+      });
+    })
+    .then(depJson => BbPromise.try(() => JSON.parse(depJson)));
+  }
+
+  static _rebaseFileReferences(pathToPackageRoot, moduleVersion) {
+    if (/^file:[^/]{2}/.test(moduleVersion)) {
+      const filePath = _.replace(moduleVersion, /^file:/, '');
+      return _.replace(`file:${pathToPackageRoot}/${filePath}`, /\\/g, '/');
+    }
+  
+    return moduleVersion;
+  }
+  
+  static rebaseLockfile(pathToPackageRoot, lockfile) {
+    if (lockfile.version) {
+      lockfile.version = NPM._rebaseFileReferences(pathToPackageRoot, lockfile.version);
+    }
+  
+    if (lockfile.dependencies) {
+      _.forIn(lockfile.dependencies, lockedDependency => {
+        NPM.rebaseLockfile(pathToPackageRoot, lockedDependency);
+      });
+    }
+  }
+  
+  static install(cwd, maxExecBufferSize) {
+    return BbPromise.fromCallback(cb => {
+      childProcess.exec('npm install', {
+        cwd: cwd,
+        maxBuffer: maxExecBufferSize,
+        encoding: 'utf8'
+      }, cb);
+    })
+    .return();
+  }
+
+  static prune(cwd, maxExecBufferSize) {
+    return BbPromise.fromCallback(cb => {
+      childProcess.exec('npm prune', {
+        cwd: cwd,
+        maxBuffer: maxExecBufferSize,
+        encoding: 'utf8'
+      }, cb);
+    })
+    .return();
+  }
+}
+
+module.exports = NPM;
diff --git a/lib/packagers/npm.test.js b/lib/packagers/npm.test.js
new file mode 100644
index 000000000..481f134ad
--- /dev/null
+++ b/lib/packagers/npm.test.js
@@ -0,0 +1,214 @@
+'use strict';
+/**
+ * Unit tests for packagers/index
+ */
+
+const _ = require('lodash');
+const BbPromise = require('bluebird');
+const chai = require('chai');
+const sinon = require('sinon');
+const mockery = require('mockery');
+
+// Mocks
+const childProcessMockFactory = require('../../tests/mocks/child_process.mock');
+
+chai.use(require('chai-as-promised'));
+chai.use(require('sinon-chai'));
+
+const expect = chai.expect;
+
+describe('npm', () => {
+  let sandbox;
+  let npmModule;
+
+  // Mocks
+  let childProcessMock;
+
+  before(() => {
+    sandbox = sinon.sandbox.create();
+    sandbox.usingPromise(BbPromise.Promise);
+
+    childProcessMock = childProcessMockFactory.create(sandbox);
+
+    mockery.enable({ useCleanCache: true, warnOnUnregistered: false });
+    mockery.registerMock('child_process', childProcessMock);
+    npmModule = require('./npm');
+  });
+
+  after(() => {
+    mockery.disable();
+    mockery.deregisterAll();
+
+    sandbox.restore();
+  });
+
+  afterEach(() => {
+    sandbox.reset();
+  });
+
+  it('should return "package-lock.json" as lockfile name', () => {
+    expect(npmModule.lockfileName).to.equal('package-lock.json');
+  });
+
+  describe('install', () => {
+    it('should use npm install', () => {
+      childProcessMock.exec.yields(null, 'installed successfully', '');
+      return expect(npmModule.install('myPath', 2000)).to.be.fulfilled
+      .then(result => {
+        expect(result).to.be.undefined;
+        expect(childProcessMock.exec).to.have.been.calledOnce;
+        expect(childProcessMock.exec).to.have.been.calledWithExactly(
+          'npm install',
+          {
+            cwd: 'myPath',
+            encoding: 'utf8',
+            maxBuffer: 2000
+          },
+          sinon.match.any
+        );
+        return null;
+      });
+    });
+  });
+
+  describe('prune', () => {
+    it('should use npm prune', () => {
+      childProcessMock.exec.yields(null, 'success', '');
+      return expect(npmModule.prune('myPath', 2000)).to.be.fulfilled
+      .then(result => {
+        expect(result).to.be.undefined;
+        expect(childProcessMock.exec).to.have.been.calledOnce;
+        expect(childProcessMock.exec).to.have.been.calledWithExactly(
+          'npm prune',
+          {
+            cwd: 'myPath',
+            encoding: 'utf8',
+            maxBuffer: 2000
+          },
+          sinon.match.any
+        );
+        return null;
+      });
+    });
+  });
+
+  describe('getProdDependencies', () => {
+    it('should use npm ls', () => {
+      childProcessMock.exec.yields(null, '{}', '');
+      return expect(npmModule.getProdDependencies('myPath', 10, 2000)).to.be.fulfilled
+      .then(result => {
+        expect(result).to.be.an('object').that.is.empty;
+        expect(childProcessMock.exec).to.have.been.calledOnce,
+        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
+          'npm ls -prod -json -depth=10'
+        );
+        return null;
+      });
+    });
+
+    it('should default to depth 1', () => {
+      childProcessMock.exec.yields(null, '{}', '');
+      return expect(npmModule.getProdDependencies('myPath')).to.be.fulfilled
+      .then(result => {
+        expect(result).to.be.an('object').that.is.empty;
+        expect(childProcessMock.exec).to.have.been.calledOnce,
+        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
+          'npm ls -prod -json -depth=1'
+        );
+        return null;
+      });
+    });
+  });
+
+  it('should reject if npm returns critical and minor errors', () => {
+    const stderr = 'ENOENT: No such file\nnpm ERR! extraneous: sinon@2.3.8 ./babel-dynamically-entries/node_modules/serverless-webpack/node_modules/sinon\n\n';
+    childProcessMock.exec.yields(new Error('something went wrong'), '{}', stderr);
+    return expect(npmModule.getProdDependencies('myPath', 1)).to.be.rejectedWith('something went wrong')
+    .then(() => BbPromise.all([
+      // npm ls and npm prune should have been called
+      expect(childProcessMock.exec).to.have.been.calledOnce,
+      expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
+        'npm ls -prod -json -depth=1'
+      ),
+    ]));
+  });
+
+  it('should ignore minor local NPM errors and log them', () => {
+    const stderr = _.join(
+      [
+        'npm ERR! extraneous: sinon@2.3.8 ./babel-dynamically-entries/node_modules/serverless-webpack/node_modules/sinon',
+        'npm ERR! missing: internalpackage-1@1.0.0, required by internalpackage-2@1.0.0',
+        'npm ERR! peer dep missing: sinon@2.3.8',
+      ],
+      '\n'
+    );
+    const lsResult = {
+      version: '1.0.0',
+      problems: [
+        'npm ERR! extraneous: sinon@2.3.8 ./babel-dynamically-entries/node_modules/serverless-webpack/node_modules/sinon',
+        'npm ERR! missing: internalpackage-1@1.0.0, required by internalpackage-2@1.0.0',
+        'npm ERR! peer dep missing: sinon@2.3.8',
+      ],
+      dependencies: {
+        '@scoped/vendor': '1.0.0',
+        uuid: '^5.4.1',
+        bluebird: '^3.4.0'
+      }
+    };
+
+    childProcessMock.exec.yields(new Error('NPM error'), JSON.stringify(lsResult), stderr);
+    return expect(npmModule.getProdDependencies('myPath', 1)).to.be.fulfilled
+    .then(dependencies => BbPromise.all([
+      // npm ls and npm prune should have been called
+      expect(childProcessMock.exec).to.have.been.calledOnce,
+      expect(childProcessMock.exec).to.have.been.calledWith(
+        'npm ls -prod -json -depth=1'
+      ),
+      expect(dependencies).to.deep.equal(lsResult),
+    ]));
+  });
+
+  it('should rebase lock file references', () => {
+    const expectedLocalModule = 'file:../../locals/../../mymodule';
+    const fakePackageLockJSON = {
+      name: 'test-service',
+      version: '1.0.0',
+      description: 'Packaged externals for test-service',
+      private: true,
+      dependencies: {
+        '@scoped/vendor': '1.0.0',
+        uuid: {
+          version: '^5.4.1'
+        },
+        bluebird: {
+          version: '^3.4.0'
+        },
+        localmodule: {
+          version: 'file:../../mymodule'
+        }
+      }
+    };
+    const expectedPackageLockJSON = {
+      name: 'test-service',
+      version: '1.0.0',
+      description: 'Packaged externals for test-service',
+      private: true,
+      dependencies: {
+        '@scoped/vendor': '1.0.0',
+        uuid: {
+          version: '^5.4.1'
+        },
+        bluebird: {
+          version: '^3.4.0'
+        },
+        localmodule: {
+          version: expectedLocalModule
+        }
+      }
+    };
+
+    npmModule.rebaseLockfile('../../locals', fakePackageLockJSON);
+    expect(fakePackageLockJSON).to.deep.equal(expectedPackageLockJSON);
+  });
+
+});
diff --git a/package.json b/package.json
index 1b1678ab0..fe0ccaee2 100644
--- a/package.json
+++ b/package.json
@@ -24,12 +24,13 @@
   },
   "homepage": "https://github.com/serverless-heaven/serverless-webpack#readme",
   "scripts": {
-    "test": "nyc ./node_modules/mocha/bin/_mocha tests/all -R spec --recursive",
+    "test": "nyc ./node_modules/mocha/bin/_mocha tests/all \"lib/**/*.test.js\" -R spec --recursive",
     "eslint": "node node_modules/eslint/bin/eslint.js --ext .js lib"
   },
   "nyc": {
     "exclude": [
-      "tests/**/*.*"
+      "tests/**/*.*",
+      "**/*.test.js"
     ],
     "reporter": [
       "lcov",
diff --git a/tests/packExternalModules.test.js b/tests/packExternalModules.test.js
index 0c9a042db..5bb39e05f 100644
--- a/tests/packExternalModules.test.js
+++ b/tests/packExternalModules.test.js
@@ -9,7 +9,6 @@ const mockery = require('mockery');
 const Serverless = require('serverless');
 
 // Mocks
-const childProcessMockFactory = require('./mocks/child_process.mock');
 const fsExtraMockFactory = require('./mocks/fs-extra.mock');
 const packageMock = require('./mocks/package.mock.json');
 const packageLocalRefMock = require('./mocks/packageLocalRef.mock.json');
@@ -19,6 +18,20 @@ chai.use(require('sinon-chai'));
 
 const expect = chai.expect;
 
+const packagerMockFactory = {
+  create(sandbox) {
+    const packagerMock = {
+      lockfileName: 'mocked-lock.json',
+      rebaseLockfile: sandbox.stub(),
+      getProdDependencies: sandbox.stub(),
+      install: sandbox.stub(),
+      prune: sandbox.stub()
+    };
+
+    return packagerMock;
+  }
+};
+
 describe('packExternalModules', () => {
   let sandbox;
   let baseModule;
@@ -26,7 +39,8 @@ describe('packExternalModules', () => {
   let module;
 
   // Mocks
-  let childProcessMock;
+  let packagerFactoryMock;
+  let packagerMock;
   let fsExtraMock;
   // Serverless stubs
   let writeFileSyncStub;
@@ -34,14 +48,21 @@ describe('packExternalModules', () => {
 
   before(() => {
     sandbox = sinon.sandbox.create();
-    sandbox.usingPromise(BbPromise);
+    sandbox.usingPromise(BbPromise.Promise);
 
-    childProcessMock = childProcessMockFactory.create(sandbox);
+    packagerMock = packagerMockFactory.create(sandbox);
     fsExtraMock = fsExtraMockFactory.create(sandbox);
 
-    mockery.enable({ warnOnUnregistered: false });
-    mockery.registerMock('child_process', childProcessMock);
+    // Setup packager mocks
+    packagerFactoryMock = {
+      get: sinon.stub()
+    };
+    packagerFactoryMock.get.withArgs('npm').returns(packagerMock);
+    packagerFactoryMock.get.throws(new Error('Packager not mocked'));
+
+    mockery.enable({ useCleanCache: true, warnOnUnregistered: false });
     mockery.registerMock('fs-extra', fsExtraMock);
+    mockery.registerMock('./packagers', packagerFactoryMock);
     mockery.registerMock(path.join(process.cwd(), 'package.json'), packageMock);
     baseModule = require('../lib/packExternalModules');
     Object.freeze(baseModule);
@@ -50,6 +71,7 @@ describe('packExternalModules', () => {
   after(() => {
     mockery.disable();
     mockery.deregisterAll();
+    sandbox.restore();
   });
 
   beforeEach(() => {
@@ -74,13 +96,11 @@ describe('packExternalModules', () => {
 
   afterEach(() => {
     // Reset all counters and restore all stubbed functions
-    writeFileSyncStub.reset();
-    readFileSyncStub.reset();
-    childProcessMock.exec.reset();
+    writeFileSyncStub.restore();
+    readFileSyncStub.restore();
     fsExtraMock.pathExists.reset();
     fsExtraMock.copy.reset();
     sandbox.reset();
-    sandbox.restore();
   });
 
   describe('packExternalModules()', () => {
@@ -206,7 +226,7 @@ describe('packExternalModules', () => {
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
         expect(fsExtraMock.copy).to.not.have.been.called,
-        expect(childProcessMock.exec).to.not.have.been.called,
+        expect(packagerFactoryMock.get).to.not.have.been.called,
         expect(writeFileSyncStub).to.not.have.been.called,
       ]));
     });
@@ -234,9 +254,9 @@ describe('packExternalModules', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
@@ -247,16 +267,9 @@ describe('packExternalModules', () => {
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.been.calledOnce,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.have.been.calledOnce,
       ]));
     });
 
@@ -301,33 +314,16 @@ describe('packExternalModules', () => {
           }
         }
       };
-      const expectedPackageLockJSON = {
-        name: 'test-service',
-        version: '1.0.0',
-        description: 'Packaged externals for test-service',
-        private: true,
-        dependencies: {
-          '@scoped/vendor': '1.0.0',
-          uuid: {
-            version: '^5.4.1'
-          },
-          bluebird: {
-            version: '^3.4.0'
-          },
-          localmodule: {
-            version: expectedLocalModule
-          }
-        }
-      };
 
       _.set(serverless, 'service.custom.webpackIncludeModules.packagePath', path.join('locals', 'package.json'));
       module.webpackOutputPath = 'outputPath';
       readFileSyncStub.returns(fakePackageLockJSON);
       fsExtraMock.pathExists.yields(null, true);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.rebaseLockfile.callsFake((pathToPackageRoot, lockfile) => lockfile);
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = statsWithFileRef;
 
       sandbox.stub(process, 'cwd').returns(path.join('/my/Service/Path'));
@@ -338,22 +334,20 @@ describe('packExternalModules', () => {
         // The module package JSON and the composite one should have been stored
         expect(writeFileSyncStub).to.have.been.calledThrice,
         expect(writeFileSyncStub.firstCall.args[1]).to.equal(JSON.stringify(expectedCompositePackageJSON, null, 2)),
-        expect(writeFileSyncStub.secondCall.args[1]).to.equal(JSON.stringify(expectedPackageLockJSON, null, 2)),
         expect(writeFileSyncStub.thirdCall.args[1]).to.equal(JSON.stringify(expectedPackageJSON, null, 2)),
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.been.calledOnce,
+        // Lock file rebase should have been called
+        expect(packagerMock.rebaseLockfile).to.have.been.calledOnce,
+        expect(packagerMock.rebaseLockfile).to.have.been.calledWith(sinon.match.any, sinon.match(fakePackageLockJSON)),
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
-      ]));
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.have.been.calledOnce,
+      ]))
+      .finally(() => {
+        process.cwd.restore();
+      });
     });
 
     it('should skip module copy for Google provider', () => {
@@ -380,9 +374,9 @@ describe('packExternalModules', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
@@ -393,37 +387,34 @@ describe('packExternalModules', () => {
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.not.been.called,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledTwice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        )
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.not.have.been.called,
       ]));
     });
 
-    it('should reject if npm install fails', () => {
+    it('should reject if packager install fails', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(new Error('npm install failed'));
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.callsFake(() => BbPromise.reject(new Error('npm install failed')));
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.rejectedWith('npm install failed')
       .then(() => BbPromise.all([
         // npm ls and npm install should have been called
-        expect(childProcessMock.exec).to.have.been.calledTwice,
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.not.have.been.called,
       ]));
     });
 
-    it('should reject if npm returns a critical error', () => {
-      const stderr = 'ENOENT: No such file';
+    it('should reject if packager returns a critical error', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.yields(new Error('something went wrong'), '{}', stderr);
+      packagerMock.getProdDependencies.callsFake(() => BbPromise.reject(new Error('something went wrong')));
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.rejectedWith('something went wrong')
       .then(() => BbPromise.all([
@@ -432,119 +423,50 @@ describe('packExternalModules', () => {
         // The modules should have been copied
         expect(fsExtraMock.copy).to.not.have.been.called,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledOnce,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.not.have.been.called,
+        expect(packagerMock.prune).to.not.have.been.called,
       ]));
     });
 
-    it('should reject if npm returns critical and minor errors', () => {
-      const stderr = 'ENOENT: No such file\nnpm ERR! extraneous: sinon@2.3.8 ./babel-dynamically-entries/node_modules/serverless-webpack/node_modules/sinon\n\n';
+    it('should not install modules if no external modules are reported', () => {
       module.webpackOutputPath = 'outputPath';
-      fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.yields(new Error('something went wrong'), '{}', stderr);
-      module.compileStats = stats;
-      return expect(module.packExternalModules()).to.be.rejectedWith('something went wrong')
+      packagerMock.getProdDependencies.returns(BbPromise.resolve());
+      module.compileStats = noExtStats;
+      return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
         // The module package JSON and the composite one should have been stored
         expect(writeFileSyncStub).to.not.have.been.called,
         // The modules should have been copied
         expect(fsExtraMock.copy).to.not.have.been.called,
-        // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledOnce,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
+        // npm install and npm prune should not have been called
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.not.have.been.called,
+        expect(packagerMock.prune).to.not.have.been.called,
       ]));
     });
 
-    it('should ignore minor local NPM errors and log them', () => {
-      const expectedCompositePackageJSON = {
-        name: 'test-service',
-        version: '1.0.0',
-        description: 'Packaged externals for test-service',
-        private: true,
-        dependencies: {
-          '@scoped/vendor': '1.0.0',
-          uuid: '^5.4.1',
-          bluebird: '^3.4.0'
-        }
-      };
-      const expectedPackageJSON = {
-        dependencies: {
-          '@scoped/vendor': '1.0.0',
-          uuid: '^5.4.1',
-          bluebird: '^3.4.0'
-        }
-      };
-      const stderr = _.join(
-        [
-          'npm ERR! extraneous: sinon@2.3.8 ./babel-dynamically-entries/node_modules/serverless-webpack/node_modules/sinon',
-          'npm ERR! missing: internalpackage-1@1.0.0, required by internalpackage-2@1.0.0',
-          'npm ERR! peer dep missing: sinon@2.3.8',
-        ],
-        '\n'
-      );
-      const lsResult = {
-        version: '1.0.0',
-        problems: [
-          'npm ERR! extraneous: sinon@2.3.8 ./babel-dynamically-entries/node_modules/serverless-webpack/node_modules/sinon',
-          'npm ERR! missing: internalpackage-1@1.0.0, required by internalpackage-2@1.0.0',
-          'npm ERR! peer dep missing: sinon@2.3.8',
-        ],
-        dependencies: {
-          '@scoped/vendor': '1.0.0',
-          uuid: '^5.4.1',
-          bluebird: '^3.4.0'
-        }
-      };
-
+    it('should report ignored packager problems in verbose mode', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(new Error('NPM error'), JSON.stringify(lsResult), stderr);
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({
+        problems: [
+          'Problem 1',
+          'Problem 2'
+        ]
+      }));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
-      .then(() => BbPromise.all([
-        // The module package JSON and the composite one should have been stored
-        expect(writeFileSyncStub).to.have.been.calledTwice,
-        expect(writeFileSyncStub.firstCall.args[1]).to.equal(JSON.stringify(expectedCompositePackageJSON, null, 2)),
-        expect(writeFileSyncStub.secondCall.args[1]).to.equal(JSON.stringify(expectedPackageJSON, null, 2)),
-        // The modules should have been copied
-        expect(fsExtraMock.pathExists).to.have.been.calledOnce,
-        expect(fsExtraMock.copy).to.have.been.calledOnce,
-        // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
-      ]));
-    });
-
-    it('should not install modules if no external modules are reported', () => {
-      module.webpackOutputPath = 'outputPath';
-      fsExtraMock.copy.yields();
-      childProcessMock.exec.yields(null, '{}', '');
-      module.compileStats = noExtStats;
-      return expect(module.packExternalModules()).to.be.fulfilled
-      .then(() => BbPromise.all([
-        // The module package JSON and the composite one should have been stored
-        expect(writeFileSyncStub).to.not.have.been.called,
-        // The modules should have been copied
-        expect(fsExtraMock.copy).to.not.have.been.called,
-        // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledOnce,
-      ]));
+      .then(() => {
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce;
+        expect(serverless.cli.log).to.have.been.calledWith('=> Problem 1');
+        expect(serverless.cli.log).to.have.been.calledWith('=> Problem 2');
+        return null;
+      });
     });
 
     it('should install external modules when forced', () => {
@@ -576,9 +498,9 @@ describe('packExternalModules', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
@@ -589,16 +511,9 @@ describe('packExternalModules', () => {
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.been.calledOnce,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.have.been.calledOnce,
       ]));
     });
 
@@ -631,9 +546,9 @@ describe('packExternalModules', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
@@ -644,16 +559,9 @@ describe('packExternalModules', () => {
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.been.calledOnce,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.have.been.calledOnce,
       ]));
     });
 
@@ -685,9 +593,9 @@ describe('packExternalModules', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, false);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
@@ -698,16 +606,9 @@ describe('packExternalModules', () => {
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.been.calledOnce,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.have.been.calledOnce,
       ]));
     });
 
@@ -734,29 +635,25 @@ describe('packExternalModules', () => {
       module.webpackOutputPath = 'outputPath';
       fsExtraMock.pathExists.yields(null, true);
       fsExtraMock.copy.yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      readFileSyncStub.returns({ info: 'lockfile' });
+      packagerMock.rebaseLockfile.callsFake((pathToPackageRoot, lockfile) => lockfile);
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
         // The module package JSON and the composite one should have been stored
-        expect(writeFileSyncStub).to.have.been.calledTwice,
+        expect(writeFileSyncStub).to.have.been.calledThrice,
         expect(writeFileSyncStub.firstCall.args[1]).to.equal(JSON.stringify(expectedCompositePackageJSON, null, 2)),
-        expect(writeFileSyncStub.secondCall.args[1]).to.equal(JSON.stringify(expectedPackageJSON, null, 2)),
+        expect(writeFileSyncStub.secondCall.args[1]).to.equal(JSON.stringify({ info: 'lockfile' }, null, 2)),
+        expect(writeFileSyncStub.thirdCall.args[1]).to.equal(JSON.stringify(expectedPackageJSON, null, 2)),
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.been.calledOnce,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.have.been.calledOnce,
       ]));
     });
 
@@ -784,9 +681,9 @@ describe('packExternalModules', () => {
       readFileSyncStub.throws(new Error('Failed to read package-lock.json'));
       fsExtraMock.pathExists.yields(null, true);
       fsExtraMock.copy.onFirstCall().yields();
-      childProcessMock.exec.onFirstCall().yields(null, '{}', '');
-      childProcessMock.exec.onSecondCall().yields(null, '', '');
-      childProcessMock.exec.onThirdCall().yields();
+      packagerMock.getProdDependencies.returns(BbPromise.resolve({}));
+      packagerMock.install.returns(BbPromise.resolve());
+      packagerMock.prune.returns(BbPromise.resolve());
       module.compileStats = stats;
       return expect(module.packExternalModules()).to.be.fulfilled
       .then(() => BbPromise.all([
@@ -797,16 +694,9 @@ describe('packExternalModules', () => {
         // The modules should have been copied
         expect(fsExtraMock.copy).to.have.been.calledOnce,
         // npm ls and npm prune should have been called
-        expect(childProcessMock.exec).to.have.been.calledThrice,
-        expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-          'npm ls -prod -json -depth=1'
-        ),
-        expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-          'npm install'
-        ),
-        expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-          'npm prune'
-        )
+        expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+        expect(packagerMock.install).to.have.been.calledOnce,
+        expect(packagerMock.prune).to.have.been.calledOnce,
       ]));
     });
 
@@ -864,9 +754,9 @@ describe('packExternalModules', () => {
         module.webpackOutputPath = 'outputPath';
         fsExtraMock.pathExists.yields(null, false);
         fsExtraMock.copy.yields();
-        childProcessMock.exec.onFirstCall().yields(null, JSON.stringify(dependencyGraph), '');
-        childProcessMock.exec.onSecondCall().yields(null, '', '');
-        childProcessMock.exec.onThirdCall().yields();
+        packagerMock.getProdDependencies.returns(BbPromise.resolve(dependencyGraph));
+        packagerMock.install.returns(BbPromise.resolve());
+        packagerMock.prune.returns(BbPromise.resolve());
         module.compileStats = peerDepStats;
         return expect(module.packExternalModules()).to.be.fulfilled
         .then(() => BbPromise.all([
@@ -877,16 +767,9 @@ describe('packExternalModules', () => {
           // The modules should have been copied
           expect(fsExtraMock.copy).to.have.been.calledOnce,
           // npm ls and npm prune should have been called
-          expect(childProcessMock.exec).to.have.been.calledThrice,
-          expect(childProcessMock.exec.firstCall).to.have.been.calledWith(
-            'npm ls -prod -json -depth=1'
-          ),
-          expect(childProcessMock.exec.secondCall).to.have.been.calledWith(
-            'npm install'
-          ),
-          expect(childProcessMock.exec.thirdCall).to.have.been.calledWith(
-            'npm prune'
-          )
+          expect(packagerMock.getProdDependencies).to.have.been.calledOnce,
+          expect(packagerMock.install).to.have.been.calledOnce,
+          expect(packagerMock.prune).to.have.been.calledOnce,
         ]));
       });
     });