Add fileExists mock

This mock is similar to the readFile mock in that mock files can be
added to the PipelineTestHelper. If no filename is registered with the
helper, then the mock returns false by default.

README.md

@@ -185,17 +185,17 @@ You can take a look at the `BasePipelineTest` class to have the short list of al
 Some tricky methods such as `load` and `parallel` are implemented directly in the helper.
 If you want to override those, make sure that you extend the `PipelineTestHelper` class.
 
-### Mocking readFile
+### Mocking readFile and fileExists
 
-The `readFile` step can be mocked to return a specific string for a given file name. This can be useful for testing
-pipelines which must read data from a file which is required for subsequent steps. An example of such a testing scenario
-follows:
+The `readFile` and `fileExists` steps can be mocked to return a specific result for a given file name. This can be
+useful for testing pipelines for which file operations can influence subsequent steps. An example of such a testing
+scenario follows:
 
 ```groovy
 // Jenkinsfile
 node {
     stage('Process output') {
-        if (readFile('output') == 'FAILED!!!') {
+        if (fileExists('output') && readFile('output') == 'FAILED!!!') {
             currentBuild.result = 'FAILURE'
             error 'Build failed'
         }
@@ -206,6 +206,7 @@ node {
 ```groovy
 @Test
 void exampleReadFileTest() {
+    helper.addFileExistsMock('fileExists', true)
     helper.addReadFileMock('output', 'FAILED!!!')
     runScript("Jenkinsfile")
     assertJobStatusFailure()

src/main/groovy/com/lesfurets/jenkins/unit/BasePipelineTest.groovy

@@ -156,6 +156,7 @@ abstract class BasePipelineTest {
             println(message)
         })
         helper.registerAllowedMethod("error", [String], { updateBuildStatus('FAILURE') })
+        helper.registerAllowedMethod('fileExists', [String], { String arg -> helper.fileExists(arg) })
         helper.registerAllowedMethod("gatlingArchive")
         helper.registerAllowedMethod("gitlabBuilds", [Map, Closure])
         helper.registerAllowedMethod("gitlabCommitStatus", [String, Closure], { String name, Closure c ->

src/main/groovy/com/lesfurets/jenkins/unit/PipelineTestHelper.groovy

@@ -1,5 +1,7 @@
 package com.lesfurets.jenkins.unit
 
+import com.sun.org.apache.xpath.internal.operations.Bool
+
 import static com.lesfurets.jenkins.unit.MethodSignature.method
 
 import java.lang.reflect.Method
@@ -108,6 +110,8 @@ class PipelineTestHelper {
     /** Let scripts and library classes access global vars (env, currentBuild) */
     protected Binding binding
 
+    Map<String, Boolean> mockFileExistsResults = [:]
+
     Map<String, String> mockReadFileOutputs = [:]
 
     /**
@@ -299,6 +303,7 @@ class PipelineTestHelper {
         gse.setConfig(configuration)
 
         mockScriptOutputs.clear()
+        mockFileExistsResults.clear()
         mockReadFileOutputs.clear()
         return this
     }
@@ -568,6 +573,14 @@ class PipelineTestHelper {
         }
     }
 
+    void addFileExistsMock(String file, Boolean result) {
+        mockFileExistsResults[file] = result
+    }
+
+    Boolean fileExists(String arg) {
+        return mockFileExistsResults[arg] ?: false
+    }
+
     void addReadFileMock(String file, String contents) {
         mockReadFileOutputs[file] = contents
     }

src/test/groovy/com/lesfurets/jenkins/unit/PipelineTestHelperTest.groovy

@@ -39,13 +39,25 @@ class PipelineTestHelperTest {
     void readFile() {
         // given:
         def helper = new PipelineTestHelper()
-        helper.addReadFileMock('test', 'contents')
+        helper.addFileExistsMock('test', true)
 
         // when:
-        def output = helper.readFile('test')
+        def result = helper.fileExists('test')
 
         // then:
-        Assertions.assertThat(output).isEqualTo('contents')
+        Assertions.assertThat(result).isTrue()
+    }
+
+    @Test
+    void readFileNotMocked() {
+        // given:
+        def helper = new PipelineTestHelper()
+
+        // when:
+        def result = helper.fileExists('test')
+
+        // then:
+        Assertions.assertThat(result).isFalse()
     }
 
     @Test