diff --git a/gulpfile.js b/gulpfile.js
index 7534586c9..af384de83 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -28,7 +28,11 @@ const paths = {
     '!**/dev-prelude.js',
     ...IGNORED_PACKAGES,
   ],
-  packageOther: ['packages/*/*/src/**/dev-prelude.js'],
+  packageOther: [
+    'packages/*/*/src/**/dev-prelude.js',
+    // This has to have some glob syntax so that vinyl.base will be right
+    'packages/{runtimes,}/js/src/helpers/*.ts',
+  ],
   packages: 'packages/',
 };
 
diff --git a/packages/core/integration-tests/test/rust.js b/packages/core/integration-tests/test/rust.js
index 7ef66455e..79fc99177 100644
--- a/packages/core/integration-tests/test/rust.js
+++ b/packages/core/integration-tests/test/rust.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import path from 'path';
 import {
@@ -48,12 +49,14 @@ describe.skip('rust', function () {
 
     // not minified
     assert(
+      // $FlowFixMe old api, test is skipped
       (await outputFS.stat(Array.from(b.childBundles)[0].name)).size > 500,
     );
   });
 
   it('should generate a wasm file from a rust file with rustc with --target=node', async function () {
     this.timeout(500000);
+    // $FlowFixMe old api, test is skipped
     let b = await bundle(path.join(__dirname, '/integration/rust/index.js'), {
       target: 'node',
     });
@@ -84,6 +87,7 @@ describe.skip('rust', function () {
 
     // not minified
     assert(
+      // $FlowFixMe old api, test is skipped
       (await outputFS.stat(Array.from(b.childBundles)[0].name)).size > 500,
     );
   });
@@ -91,6 +95,7 @@ describe.skip('rust', function () {
   it('should support rust files with dependencies via rustc', async function () {
     this.timeout(500000);
     let b = bundler(path.join(__dirname, '/integration/rust-deps/index.js'));
+    // $FlowFixMe old api, test is skipped
     let bundle = await b.bundle();
 
     await assertBundleTree(bundle, {
diff --git a/packages/core/integration-tests/test/schema-jsonld.js b/packages/core/integration-tests/test/schema-jsonld.js
index faaf9641b..cdd9ff867 100644
--- a/packages/core/integration-tests/test/schema-jsonld.js
+++ b/packages/core/integration-tests/test/schema-jsonld.js
@@ -1,3 +1,4 @@
+// @flow
 import {
   assertBundles,
   bundle,
@@ -14,7 +15,9 @@ describe.v2('jsonld', function () {
     let b = await bundle(
       path.join(__dirname, '/integration/schema-jsonld/index.html'),
       {
-        publicURL: 'https://place.holder/',
+        defaultTargetOptions: {
+          publicUrl: 'https://place.holder/',
+        },
       },
     );
 
@@ -47,25 +50,29 @@ describe.v2('jsonld', function () {
     );
     let contentBetweenScriptTag = new RegExp(
       /<\s*script \s*type="application\/ld\+json"\s*>(.*)<\/\s*script\s*>/gm,
-    ).exec(file)[1];
+    ).exec(file)?.[1];
 
     let jsonldData = assertValidJsonObject(contentBetweenScriptTag);
-    match(jsonldData.logo.url, /logo\.[a-f0-9]+\.png/);
-    match(jsonldData.image[0], /image\.[a-f0-9]+\.jpeg/);
-    match(jsonldData.image[1], /image\.[a-f0-9]+\.jpeg/);
+    match(jsonldData?.logo.url, /logo\.[a-f0-9]+\.png/);
+    match(jsonldData?.image[0], /image\.[a-f0-9]+\.jpeg/);
+    match(jsonldData?.image[1], /image\.[a-f0-9]+\.jpeg/);
   });
 });
 
-function match(test, pattern) {
+function match(test?: string, pattern: RegExp | string) {
+  if (!test) return assert.fail();
   let success = new RegExp(pattern).test(test);
   if (success) {
-    assert.ok(`'${test}' matched the given pattern of '${pattern}'`);
+    assert.ok(`'${test}' matched the given pattern of '${pattern.toString()}'`);
     return;
   }
-  assert.fail(`'${test}' did not match the given pattern of '${pattern}'`);
+  assert.fail(
+    `'${test}' did not match the given pattern of '${pattern.toString()}'`,
+  );
 }
 
-function assertValidJsonObject(dataAsString) {
+function assertValidJsonObject(dataAsString?: string) {
+  if (!dataAsString) return assert.fail();
   try {
     let data = JSON.parse(dataAsString);
     assert.ok('input string is a valid json object');
diff --git a/packages/core/integration-tests/test/svg.js b/packages/core/integration-tests/test/svg.js
index 1b51ecd65..a1c2604c5 100644
--- a/packages/core/integration-tests/test/svg.js
+++ b/packages/core/integration-tests/test/svg.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import {
   assertBundles,
@@ -52,51 +53,59 @@ describe('svg', function () {
       },
     ]);
 
-    let file = await outputFS.readFile(
-      b.getBundles().find((b) => b.type === 'svg').filePath,
-      'utf-8',
-    );
+    let svgBundle = b.getBundles().find((b) => b.type === 'svg');
+    if (!svgBundle) return assert.fail();
+
+    let file = await outputFS.readFile(svgBundle.filePath, 'utf-8');
     assert(file.includes('<a href="/other1.html">'));
     assert(file.includes('<use href="#circle"'));
+
+    let squareBundle = b.getBundles().find((b) => b.name.startsWith('square'));
+    if (!squareBundle) return assert.fail();
+
     assert(
       file.includes(
-        `<use xlink:href="/${path.basename(
-          b.getBundles().find((b) => b.name.startsWith('square')).filePath,
-        )}#square"`,
+        `<use xlink:href="/${path.basename(squareBundle.filePath)}#square"`,
       ),
     );
+
+    let gradientBundle = b
+      .getBundles()
+      .find((b) => b.name.startsWith('gradient'));
+    if (!gradientBundle) return assert.fail();
+
     assert(
       file.includes(
-        `fill="url('/${path.basename(
-          b.getBundles().find((b) => b.name.startsWith('gradient')).filePath,
-        )}#myGradient')"`,
+        `fill="url('/${path.basename(gradientBundle.filePath)}#myGradient')"`,
       ),
     );
+
+    let scriptBundle = b
+      .getBundles()
+      .find((b) => b.type === 'js' && b.env.sourceType === 'script');
+    if (!scriptBundle) return assert.fail();
+
     assert(
       file.includes(
-        `<script xlink:href="/${path.basename(
-          b
-            .getBundles()
-            .find((b) => b.type === 'js' && b.env.sourceType === 'script')
-            .filePath,
-        )}"`,
+        `<script xlink:href="/${path.basename(scriptBundle.filePath)}"`,
       ),
     );
+
+    let moduleBundle = b
+      .getBundles()
+      .find((b) => b.type === 'js' && b.env.sourceType === 'module');
+    if (!moduleBundle) return assert.fail();
+
     assert(
-      file.includes(
-        `<script href="/${path.basename(
-          b
-            .getBundles()
-            .find((b) => b.type === 'js' && b.env.sourceType === 'module')
-            .filePath,
-        )}"`,
-      ),
+      file.includes(`<script href="/${path.basename(moduleBundle.filePath)}"`),
     );
+
+    let cssBundle = b.getBundles().find((b) => b.type === 'css');
+    if (!cssBundle) return assert.fail();
+
     assert(
       file.includes(
-        `<?xml-stylesheet href="/${path.basename(
-          b.getBundles().find((b) => b.type === 'css').filePath,
-        )}"?>`,
+        `<?xml-stylesheet href="/${path.basename(cssBundle.filePath)}"?>`,
       ),
     );
   });
@@ -108,10 +117,10 @@ describe('svg', function () {
       },
     });
 
-    let file = await outputFS.readFile(
-      b.getBundles().find((b) => b.type === 'svg').filePath,
-      'utf-8',
-    );
+    let svgBundle = b.getBundles().find((b) => b.type === 'svg');
+    if (!svgBundle) return assert.fail();
+
+    let file = await outputFS.readFile(svgBundle.filePath, 'utf-8');
     assert(!file.includes('comment'));
   });
 
@@ -125,10 +134,10 @@ describe('svg', function () {
       },
     );
 
-    let file = await outputFS.readFile(
-      b.getBundles().find((b) => b.type === 'svg').filePath,
-      'utf-8',
-    );
+    let svgBundle = b.getBundles().find((b) => b.type === 'svg');
+    if (!svgBundle) return assert.fail();
+
+    let file = await outputFS.readFile(svgBundle.filePath, 'utf-8');
     assert(!file.includes('inkscape'));
     assert(file.includes('comment'));
   });
@@ -155,10 +164,10 @@ describe('svg', function () {
         },
       ]);
 
-      let file = await outputFS.readFile(
-        b.getBundles().find((b) => b.type === 'svg').filePath,
-        'utf-8',
-      );
+      let svgBundle = b.getBundles().find((b) => b.type === 'svg');
+      if (!svgBundle) return assert.fail();
+
+      let file = await outputFS.readFile(svgBundle.filePath, 'utf-8');
 
       assert(file.includes('<?xml-stylesheet'));
       assert(file.includes('<?xml-not-a-stylesheet'));
@@ -197,10 +206,16 @@ describe('svg', function () {
 
     assert(!svg.includes('@import'));
     assert(svg.includes(':root {\n  fill: red;\n}'));
+
+    let gradientBundle = b
+      .getBundles()
+      .find((b) => b.name.startsWith('gradient'));
+    if (!gradientBundle) return assert.fail();
+
     assert(
       svg.includes(
         `"fill: url(&quot;${path.basename(
-          b.getBundles().find((b) => b.name.startsWith('gradient')).filePath,
+          gradientBundle.filePath,
         )}#myGradient&quot;)`,
       ),
     );
diff --git a/packages/core/integration-tests/test/ts-types.js b/packages/core/integration-tests/test/ts-types.js
index fbbfa5598..515234afd 100644
--- a/packages/core/integration-tests/test/ts-types.js
+++ b/packages/core/integration-tests/test/ts-types.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import path from 'path';
 import {
diff --git a/packages/core/integration-tests/test/ts-validation.js b/packages/core/integration-tests/test/ts-validation.js
index 88998d04e..bd0697a43 100644
--- a/packages/core/integration-tests/test/ts-validation.js
+++ b/packages/core/integration-tests/test/ts-validation.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import path from 'path';
 import {
@@ -94,6 +95,7 @@ describe.v2('ts-validator', function () {
     subscription = await b.watch();
     let buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildFailure');
+    if (!buildEvent.diagnostics) return assert.fail();
     assert.equal(buildEvent.diagnostics.length, 1);
     assert.equal(
       buildEvent.diagnostics[0].message,
@@ -106,6 +108,7 @@ describe.v2('ts-validator', function () {
     );
     buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildSuccess');
+    if (!buildEvent.bundleGraph) return assert.fail();
     let output = await run(buildEvent.bundleGraph);
     assert.equal(output.message, 'The type error is fixed!');
 
@@ -115,6 +118,7 @@ describe.v2('ts-validator', function () {
     );
     buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildFailure');
+    if (!buildEvent.diagnostics) return assert.fail();
     assert.equal(buildEvent.diagnostics.length, 1);
     assert.equal(
       buildEvent.diagnostics[0].message,
@@ -146,6 +150,7 @@ describe.v2('ts-validator', function () {
 
     let buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildSuccess');
+    if (!buildEvent.bundleGraph) return assert.fail();
     let output = await run(buildEvent.bundleGraph);
     assert.equal(output.output, 'My Message!');
 
@@ -162,6 +167,7 @@ describe.v2('ts-validator', function () {
 
     buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildSuccess');
+    if (!buildEvent.bundleGraph) return assert.fail();
     output = await run(buildEvent.bundleGraph);
     assert.equal(output.output, 123456);
   });
@@ -190,6 +196,7 @@ describe.v2('ts-validator', function () {
 
     let buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildFailure');
+    if (!buildEvent.diagnostics) return assert.fail();
     assert.equal(buildEvent.diagnostics.length, 2);
     assert.equal(
       buildEvent.diagnostics[1].message,
@@ -209,6 +216,7 @@ describe.v2('ts-validator', function () {
 
     buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildFailure');
+    if (!buildEvent.diagnostics) return assert.fail();
     assert.equal(buildEvent.diagnostics.length, 1);
     assert.equal(
       buildEvent.diagnostics[0].message,
@@ -240,6 +248,7 @@ describe.v2('ts-validator', function () {
 
     let buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildSuccess');
+    if (!buildEvent.bundleGraph) return assert.fail();
     let output = await run(buildEvent.bundleGraph);
     assert.equal(output.output, 'My Message!');
 
@@ -250,6 +259,7 @@ describe.v2('ts-validator', function () {
 
     buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildFailure');
+    if (!buildEvent.diagnostics) return assert.fail();
     assert.equal(buildEvent.diagnostics.length, 1);
     assert.equal(
       buildEvent.diagnostics[0].message,
diff --git a/packages/core/integration-tests/test/watcher.js b/packages/core/integration-tests/test/watcher.js
index 24c3e439d..6ec393aa3 100644
--- a/packages/core/integration-tests/test/watcher.js
+++ b/packages/core/integration-tests/test/watcher.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import nodeFS from 'fs';
 import path from 'path';
@@ -36,20 +37,24 @@ describe.v2('watcher', function () {
     await outputFS.writeFile(
       path.join(inputDir, '/index.js'),
       'module.exports = "hello"',
-      'utf8',
+      {encoding: 'utf8'},
     );
     let b = bundler(path.join(inputDir, '/index.js'), {inputFS: overlayFS});
     subscription = await b.watch();
     let buildEvent = await getNextBuild(b);
+    if (!buildEvent.bundleGraph) return assert.fail();
+
     let output = await run(buildEvent.bundleGraph);
     assert.equal(output, 'hello');
 
     await outputFS.writeFile(
       path.join(inputDir, '/index.js'),
       'module.exports = "something else"',
-      'utf8',
+      {encoding: 'utf8'},
     );
     buildEvent = await getNextBuild(b);
+    if (!buildEvent.bundleGraph) return assert.fail();
+
     output = await run(buildEvent.bundleGraph);
     assert.equal(output, 'something else');
   });
@@ -59,7 +64,7 @@ describe.v2('watcher', function () {
     await outputFS.writeFile(
       path.join(inputDir, '/index.js'),
       'syntax\\error',
-      'utf8',
+      {encoding: 'utf8'},
     );
     let b = bundler(path.join(inputDir, '/index.js'), {inputFS: overlayFS});
     subscription = await b.watch();
@@ -68,9 +73,10 @@ describe.v2('watcher', function () {
     await outputFS.writeFile(
       path.join(inputDir, '/index.js'),
       'module.exports = "hello"',
-      'utf8',
+      {encoding: 'utf8'},
     );
     buildEvent = await getNextBuild(b);
+    if (!buildEvent.bundleGraph) return assert.fail();
     let output = await run(buildEvent.bundleGraph);
 
     assert.equal(output, 'hello');
@@ -142,7 +148,9 @@ describe.v2('watcher', function () {
   it.skip('should re-generate bundle tree when files change', async function () {
     await ncp(path.join(__dirname, '/integration/dynamic-hoist'), inputDir);
 
+    // $FlowFixMe deprecated API, test is skipped
     let b = bundler(path.join(inputDir, '/index.js'), {watch: true});
+    // $FlowFixMe deprecated API, test is skipped
     let bundle = await b.bundle();
 
     await assertBundleTree(bundle, {
@@ -226,8 +234,10 @@ describe.v2('watcher', function () {
 
   it.skip('should only re-package bundles that changed', async function () {
     await ncp(path.join(__dirname, '/integration/dynamic-hoist'), inputDir);
+    // $FlowFixMe deprecated API, test is skipped
     let b = bundler(path.join(inputDir, '/index.js'), {watch: true});
 
+    // $FlowFixMe deprecated API, test is skipped
     await b.bundle();
     let mtimes = (await fs.readdir(path.join(__dirname, '/dist'))).map(
       (f) =>
@@ -255,8 +265,10 @@ describe.v2('watcher', function () {
 
   it.skip('should unload assets that are orphaned', async function () {
     await ncp(path.join(__dirname, '/integration/dynamic-hoist'), inputDir);
+    // $FlowFixMe deprecated API, test is skipped
     let b = bundler(path.join(inputDir, '/index.js'), {watch: true});
 
+    // $FlowFixMe deprecated API, test is skipped
     let bundle = await b.bundle();
     await assertBundleTree(bundle, {
       name: 'index.js',
@@ -295,6 +307,7 @@ describe.v2('watcher', function () {
     let output = await run(bundle);
     assert.equal(await output(), 7);
 
+    // $FlowFixMe deprecated API, test is skipped
     assert(b.loadedAssets.has(path.join(inputDir, '/common-dep.js')));
 
     // Get rid of common-dep.js
@@ -338,13 +351,16 @@ describe.v2('watcher', function () {
     output = await run(bundle);
     assert.equal(await output(), 13);
 
+    // $FlowFixMe deprecated API, test is skipped
     assert(!b.loadedAssets.has(path.join(inputDir, 'common-dep.js')));
   });
 
   it.skip('should recompile all assets when a config file changes', async function () {
     await ncp(path.join(__dirname, '/integration/babel'), inputDir);
+    // $FlowFixMe deprecated API, test is skipped
     let b = bundler(path.join(inputDir, 'index.js'), {watch: true});
 
+    // $FlowFixMe deprecated API, test is skipped
     await b.bundle();
     let file = await fs.readFile(
       path.join(__dirname, '/dist/index.js'),
@@ -381,10 +397,12 @@ describe.v2('watcher', function () {
         path.join(inputDir, 'src/symlinked_local.js'),
       );
 
+      // $FlowFixMe deprecated API, test is skipped
       let b = bundler(path.join(inputDir, '/src/index.js'), {
         watch: true,
       });
 
+      // $FlowFixMe deprecated API, test is skipped
       let bundle = await b.bundle();
       let output = await run(bundle);
 
@@ -417,10 +435,13 @@ describe.v2('watcher', function () {
     let b = bundler(indexPath, {inputFS: overlayFS});
     let bundleGraph;
     subscription = await b.watch((err, event) => {
+      if (!event) return assert.fail();
       assert(event.type === 'buildSuccess');
       bundleGraph = event.bundleGraph;
     });
     await getNextBuild(b);
+
+    if (!bundleGraph) return assert.fail();
     assertBundles(bundleGraph, [
       {
         name: 'index.js',
@@ -443,6 +464,8 @@ describe.v2('watcher', function () {
     );
 
     await getNextBuild(b);
+    if (!bundleGraph) return assert.fail();
+
     assertBundles(bundleGraph, [
       {
         name: 'index.js',
@@ -461,6 +484,8 @@ describe.v2('watcher', function () {
     await outputFS.writeFile(indexPath, '');
 
     await getNextBuild(b);
+    if (!bundleGraph) return assert.fail();
+
     assertBundles(bundleGraph, [
       {
         name: 'index.js',
@@ -474,7 +499,7 @@ describe.v2('watcher', function () {
     await outputFS.writeFile(
       path.join(inputDir, '/index.js'),
       'import {other} from "./other";\nexport default other;',
-      'utf8',
+      {encoding: 'utf8'},
     );
 
     let b = bundler(path.join(inputDir, 'index.js'), {inputFS: overlayFS});
@@ -485,11 +510,12 @@ describe.v2('watcher', function () {
     await outputFS.writeFile(
       path.join(inputDir, '/other.js'),
       'export const other = 2;',
-      'utf8',
+      {encoding: 'utf8'},
     );
 
     buildEvent = await getNextBuild(b);
     assert.equal(buildEvent.type, 'buildSuccess');
+    if (!buildEvent.bundleGraph) return assert.fail();
 
     let res = await run(buildEvent.bundleGraph);
     assert.equal(res.default, 2);
diff --git a/packages/core/integration-tests/test/webmanifest.js b/packages/core/integration-tests/test/webmanifest.js
index 27a75fe2e..9a2f14c87 100644
--- a/packages/core/integration-tests/test/webmanifest.js
+++ b/packages/core/integration-tests/test/webmanifest.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import path from 'path';
 import {
@@ -43,8 +44,13 @@ describe.v2('webmanifest', function () {
       },
     ]);
 
+    const webmanifestBundle = b
+      .getBundles()
+      .find((b) => b.type === 'webmanifest');
+    if (!webmanifestBundle) return assert.fail();
+
     const manifest = await outputFS.readFile(
-      b.getBundles().find((b) => b.type === 'webmanifest').filePath,
+      webmanifestBundle.filePath,
       'utf8',
     );
     assert(/screenshot\.[0-9a-f]+\.png/.test(manifest));
@@ -85,8 +91,13 @@ describe.v2('webmanifest', function () {
       },
     ]);
 
+    const webmanifestBundle = b
+      .getBundles()
+      .find((b) => b.type === 'webmanifest');
+    if (!webmanifestBundle) return assert.fail();
+
     const manifest = await outputFS.readFile(
-      b.getBundles().find((b) => b.type === 'webmanifest').filePath,
+      webmanifestBundle.filePath,
       'utf8',
     );
     assert(/screenshot\.[0-9a-f]+\.png/.test(manifest));
diff --git a/packages/core/integration-tests/test/xml.js b/packages/core/integration-tests/test/xml.js
index 543530142..a4fa3d5b1 100644
--- a/packages/core/integration-tests/test/xml.js
+++ b/packages/core/integration-tests/test/xml.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import path from 'path';
 import {
@@ -40,18 +41,24 @@ describe.v2('xml', function () {
     ]);
 
     let contents = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+
+    let xslBundle = b.getBundles().find((b) => b.type === 'xsl');
+    if (!xslBundle) return assert.fail();
+
     assert(
       contents.includes(
         `<?xml-stylesheet type="text/xsl" href="http://example.org/${path.basename(
-          b.getBundles().find((b) => b.type === 'xsl').filePath,
+          xslBundle.filePath,
         )}"?>`,
       ),
     );
+
+    let pngBundle = b.getBundles().find((b) => b.type === 'png');
+    if (!pngBundle) return assert.fail();
+
     assert(
       contents.includes(
-        `<img src="http://example.org/${path.basename(
-          b.getBundles().find((b) => b.type === 'png').filePath,
-        )}"/>`,
+        `<img src="http://example.org/${path.basename(pngBundle.filePath)}"/>`,
       ),
     );
     assert(contents.includes(`<link href="http://example.org/post.html"/>`));
@@ -91,18 +98,24 @@ describe.v2('xml', function () {
     ]);
 
     let contents = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+
+    let xslBundle = b.getBundles().find((b) => b.type === 'xsl');
+    if (!xslBundle) return assert.fail();
+
     assert(
       contents.includes(
         `<?xml-stylesheet type="text/xsl" href="http://example.org/${path.basename(
-          b.getBundles().find((b) => b.type === 'xsl').filePath,
+          xslBundle.filePath,
         )}"?>`,
       ),
     );
+
+    let pngBundle = b.getBundles().find((b) => b.type === 'png');
+    if (!pngBundle) return assert.fail();
+
     assert(
       contents.includes(
-        `<img src="http://example.org/${path.basename(
-          b.getBundles().find((b) => b.type === 'png').filePath,
-        )}"/>`,
+        `<img src="http://example.org/${path.basename(pngBundle.filePath)}"/>`,
       ),
     );
     assert(
@@ -141,10 +154,14 @@ describe.v2('xml', function () {
     ]);
 
     let contents = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+
+    let pngBundle = b.getBundles().find((b) => b.type === 'png');
+    if (!pngBundle) return assert.fail();
+
     assert(
       contents.includes(
         `&lt;img src="http://example.org/${path.basename(
-          b.getBundles().find((b) => b.type === 'png').filePath,
+          pngBundle.filePath,
         )}">`,
       ),
     );
diff --git a/packages/core/utils/test/sourcemap.test.js b/packages/core/utils/test/sourcemap.test.js
index ba31bb0b4..31d1d87e3 100644
--- a/packages/core/utils/test/sourcemap.test.js
+++ b/packages/core/utils/test/sourcemap.test.js
@@ -1,3 +1,4 @@
+// @flow
 import assert from 'assert';
 import {
   matchSourceMappingURL,
@@ -46,6 +47,8 @@ describe('loadSourceMap', () => {
     let contents = fs.readFileSync(filename, 'utf-8');
 
     let foundMap = await loadSourceMapUrl(fs, filename, contents);
+    if (!foundMap) return assert.fail();
+
     assert.equal(foundMap.url, 'file://referenced-min.js.map');
     assert.equal(
       foundMap.filename,
@@ -65,6 +68,8 @@ describe('loadSourceMap', () => {
     let contents = fs.readFileSync(filename, 'utf-8');
 
     let foundMap = await loadSourceMapUrl(fs, filename, contents);
+    if (!foundMap) return assert.fail();
+
     assert.equal(
       foundMap.url,
       'data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjoiIiwic291cmNlcyI6WyJmb28uanMiLCJiYXIuanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6Ijs7Ozs7Ozs7O1VBQ0c7Ozs7Ozs7Ozs7Ozs7O3NCQ0RIO3NCQUNBIn0=',
@@ -88,7 +93,7 @@ describe('loadSourceMap', () => {
       projectRoot: __dirname,
     });
 
-    assert(!!map);
+    if (!map) return assert.fail();
 
     let parsedMap = map.getMap();
     assert.deepEqual(parsedMap.sources, ['input/sourcemap/referenced.js']);
@@ -184,7 +189,7 @@ describe('loadSourceMap', () => {
       projectRoot: __dirname,
     });
 
-    assert(!!map);
+    if (!map) return assert.fail();
 
     let parsedMap = map.getMap();
     assert.deepEqual(parsedMap.sources, ['input/sourcemap/referenced.js']);
@@ -199,7 +204,7 @@ describe('loadSourceMap', () => {
       projectRoot: __dirname,
     });
 
-    assert(!!map);
+    if (!map) return assert.fail();
 
     let parsedMap = map.getMap();
     assert.deepEqual(parsedMap.sources, ['input/source.js']);