Run pyenv to assert the pyenv root path exists

To support Windows (which will be done in a subsequent commit), we'll
need to translate Windows-style paths to Cygwin-style paths (for
example, C:\foo\bar -> /c/foo/bar). The fileExists step only supports
Windows-style paths when run on Windows, which means that we need to
actually run pyenv to assert that it exists.

src/com/ableton/Pyenv.groovy

@@ -120,8 +120,8 @@ class Pyenv implements Serializable {
   protected void assertPyenvRoot() {
     assert pyenvRoot
 
-    if (!script.fileExists(pyenvRoot)) {
-      script.error "pyenv root path '${pyenvRoot}' does not exist"
+    if (script.sh(returnStatus: true, script: "${pyenvRoot}/bin/pyenv --version")) {
+      script.error "pyenv executable not found in '${pyenvRoot}'"
     }
   }
 }

test/com/ableton/PyenvTest.groovy

@@ -35,8 +35,8 @@ class PyenvTest extends BasePipelineTest {
   @Test
   void assertPyenvRootInvalidRoot() {
     String pyenvRoot = '/mock/pyenv/root'
-    helper.registerAllowedMethod('fileExists', [String]) { return false }
     helper.registerAllowedMethod('isUnix', []) { return true }
+    helper.addShMock("${pyenvRoot}/bin/pyenv --version", '1.2.3', 0)
 
     assertThrows(Exception) { new Pyenv(script, '1.2.3', pyenvRoot).createVirtualEnv() }
   }
@@ -52,8 +52,8 @@ class PyenvTest extends BasePipelineTest {
   void createVirtualEnv() {
     String pythonVersion = '1.2.3'
     String pyenvRoot = '/mock/pyenv/root'
-    helper.registerAllowedMethod('fileExists', [String]) { return true }
     helper.registerAllowedMethod('isUnix', []) { return true }
+    helper.addShMock("${pyenvRoot}/bin/pyenv --version", '1.2.3', 0)
     helper.addShMock(installCommands(pyenvRoot, pythonVersion), '', 0)
 
     Object venv = new Pyenv(script, pyenvRoot).createVirtualEnv(pythonVersion, 1)
@@ -74,7 +74,6 @@ class PyenvTest extends BasePipelineTest {
     String pyenvRoot = '/mock/pyenv/root'
     boolean errorCalled = false
     helper.registerAllowedMethod('error', [String]) { errorCalled = true }
-    helper.registerAllowedMethod('fileExists', [String]) { return true }
     helper.registerAllowedMethod('isUnix', []) { return true }
     helper.addShMock("${pyenvRoot}/bin/pyenv --version", '1.2.3', 0)
     helper.addShMock(installCommands(pyenvRoot, pythonVersion), '', 1)
@@ -93,8 +92,8 @@ class PyenvTest extends BasePipelineTest {
   2.3.7
 '''
     String pyenvRoot = '/pyenv'
+    helper.addShMock("${pyenvRoot}/bin/pyenv --version", '1.2.3', 0)
     helper.addShMock("${pyenvRoot}/bin/pyenv install --list", mockPyenvVersions, 0)
-    helper.registerAllowedMethod('fileExists', [String]) { return true }
     helper.registerAllowedMethod('isUnix', []) { return true }
 
     assertTrue(new Pyenv(script, pyenvRoot).versionSupported('2.1.3'))