Added a part of RetrieveChangedFilesTest test cases

Yet to add cases for retrieving and checking test targets

scripts/src/javatests/org/oppia/android/scripts/ci/BUILD.bazel

@@ -31,3 +31,17 @@ kt_jvm_test(
         "//third_party:org_jetbrains_kotlin_kotlin-test-junit",
     ],
 )
+
+kt_jvm_test(
+    name = "RetrieveChangedFilesTest",
+    srcs = ["RetrieveChangedFilesTest.kt"],
+    deps = [
+        "//scripts:test_file_check_assets",
+        "//scripts/src/java/org/oppia/android/scripts/ci:retrieve_changed_files_lib",
+        "//scripts/src/java/org/oppia/android/scripts/common:proto_string_encoder",
+        "//scripts/src/java/org/oppia/android/scripts/testing:test_bazel_workspace",
+        "//testing:assertion_helpers",
+        "//third_party:com_google_truth_truth",
+        "//third_party:org_jetbrains_kotlin_kotlin-test-junit",
+    ],
+)

scripts/src/javatests/org/oppia/android/scripts/ci/RetrieveChangedFilesTest.kt

@@ -0,0 +1,139 @@
+package org.oppia.android.scripts.ci
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.After
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.rules.TemporaryFolder
+import org.oppia.android.scripts.common.CommandExecutor
+import org.oppia.android.scripts.common.CommandExecutorImpl
+import org.oppia.android.scripts.common.ProtoStringEncoder.Companion.toCompressedBase64
+import org.oppia.android.scripts.common.ScriptBackgroundCoroutineDispatcher
+import org.oppia.android.scripts.proto.ChangedFilesBucket
+import org.oppia.android.scripts.testing.TestBazelWorkspace
+import org.oppia.android.testing.assertThrows
+import java.io.ByteArrayOutputStream
+import java.io.File
+import java.io.OutputStream
+import java.io.PrintStream
+import java.util.concurrent.TimeUnit
+
+/** Tests for the retrieve_changed_files utility. */
+// FunctionName: test names are conventionally named with underscores.
+@Suppress("FunctionName")
+class RetrieveChangedFilesTest {
+  @field:[Rule JvmField] val tempFolder = TemporaryFolder()
+
+  private val scriptBgDispatcher by lazy { ScriptBackgroundCoroutineDispatcher() }
+  private lateinit var commandExecutor: CommandExecutor
+  private lateinit var testBazelWorkspace: TestBazelWorkspace
+  private lateinit var pendingOutputStream: ByteArrayOutputStream
+  private lateinit var originalStandardOutputStream: OutputStream
+
+  @Before
+  fun setUp() {
+    commandExecutor = initializeCommandExecutorWithLongProcessWaitTime()
+    testBazelWorkspace = TestBazelWorkspace(tempFolder)
+
+    // Redirect script output for testing purposes.
+    pendingOutputStream = ByteArrayOutputStream()
+    originalStandardOutputStream = System.out
+    System.setOut(PrintStream(pendingOutputStream))
+  }
+
+  @After
+  fun tearDown() {
+    // Reinstate test output redirection.
+    System.setOut(PrintStream(pendingOutputStream))
+
+    // Print the status of the git repository to help with debugging in the cases of test failures
+    // and to help manually verify the expect git state at the end of each test.
+    println("git status (at end of test):")
+
+    scriptBgDispatcher.close()
+  }
+
+  @Test
+  fun testUtility_noArguments_printsUsageStringAndExits() {
+    val exception = assertThrows<SecurityException>() { runScript() }
+
+    // Bazel catches the System.exit() call and throws a SecurityException. This is a bit hacky way
+    // to verify that System.exit() is called, but it's helpful.
+    assertThat(exception).hasMessageThat().contains("System.exit()")
+    assertThat(pendingOutputStream.toString()).contains("Usage:")
+  }
+
+  @Test
+  fun testUtility_invalidArguments_printsUsageStringAndExits() {
+    for (argCount in 0..4) {
+      val args = Array(argCount) { "arg${it + 1}" }
+      val exception = assertThrows<SecurityException> { runScript(*args) }
+
+      // Bazel catches the System.exit() call and throws a SecurityException.
+      assertThat(exception).hasMessageThat().contains("System.exit()")
+      assertThat(pendingOutputStream.toString()).contains("Usage:")
+    }
+  }
+
+  @Test
+  fun testUtility_invalidBase64_throwsException() {
+    assertThrows<IllegalArgumentException>() { runScript("${tempFolder.root}", "badbase64", "file1", "file2", "file3") }
+  }
+
+  @Test
+  fun testUtility_validBase64_oneTest_writesCacheNameFile() {
+    val cacheNameFilePath = tempFolder.getNewTempFilePath("cache_name")
+    val changedFilePath = tempFolder.getNewTempFilePath("changed_file_list")
+    val testTargetFilePath = tempFolder.getNewTempFilePath("test_target_list")
+    val base64String = computeBase64String(
+      ChangedFilesBucket.newBuilder().apply {
+        cacheBucketName = "example"
+        addChangedFiles("//example/to/a/file/Demonstration.kt")
+      }.build()
+    )
+
+    runScript(tempFolder.root.absolutePath, base64String, cacheNameFilePath, changedFilePath, testTargetFilePath)
+
+    assertThat(File(cacheNameFilePath).readText().trim()).isEqualTo("example")
+  }
+
+  @Test
+  fun testUtility_validBase64_oneTest_writesChangedFilePathWithCorrectFile() {
+    val cacheNameFilePath = tempFolder.getNewTempFilePath("cache_name")
+    val changedFilePath = tempFolder.getNewTempFilePath("changed_file_list")
+    val testTargetFilePath = tempFolder.getNewTempFilePath("test_target_list")
+    val base64String = computeBase64String(
+      ChangedFilesBucket.newBuilder().apply {
+        cacheBucketName = "example"
+        addChangedFiles("//example/to/a/file/Demonstration.kt")
+      }.build()
+    )
+
+    runScript(tempFolder.root.absolutePath, base64String, cacheNameFilePath, changedFilePath, testTargetFilePath)
+
+    assertThat(File(changedFilePath).readText().trim()).isEqualTo(
+      "//example/to/a/file/Demonstration.kt"
+    )
+  }
+
+  private fun runScript(vararg args: String) {
+    main(args.toList().toTypedArray())
+  }
+
+  private fun computeBase64String(changedFilesBucket: ChangedFilesBucket): String =
+    changedFilesBucket.toCompressedBase64()
+
+  /**
+   * Returns the absolute file path of a new file that can be written under this [TemporaryFolder]
+   * (but does not create the file).
+   */
+  private fun TemporaryFolder.getNewTempFilePath(name: String) =
+    File(tempFolder.root, name).absolutePath
+
+  private fun initializeCommandExecutorWithLongProcessWaitTime(): CommandExecutorImpl {
+    return CommandExecutorImpl(
+      scriptBgDispatcher, processTimeout = 5, processTimeoutUnit = TimeUnit.MINUTES
+    )
+  }
+}