fix(amazonq): enable syntax highlighting when viewing diff for generated unit tests

.changes/next-release/bugfix-3b7843b4-9673-4afa-90e8-7c4278f0d0fe.json

@@ -0,0 +1,4 @@
+{
+  "type" : "bugfix",
+  "description" : "Enable syntax highlighting when viewing diff for /test"
+}

plugins/amazonq/chat/jetbrains-community/src/software/aws/toolkits/jetbrains/services/amazonqCodeTest/controller/CodeTestChatController.kt

@@ -458,6 +458,10 @@ class CodeTestChatController(
         when (message.actionID) {
             "utg_view_diff" -> {
                 withContext(EDT) {
+                    // virtual file only needed for syntax highlighting when viewing diff
+                    val tempPath = Files.createTempFile(null, ".${session.testFileName.substringAfterLast('.')}")
+                    val virtualFile = tempPath.toFile().toVirtualFile()
+
                     (DiffManager.getInstance() as DiffManagerEx).showDiffBuiltin(
                         context.project,
                         SimpleDiffRequest(
@@ -466,13 +470,18 @@ class CodeTestChatController(
                                 getFileContentAtTestFilePath(
                                     session.projectRoot,
                                     session.testFileRelativePathToProjectRoot
-                                )
+                                ),
+                                virtualFile
+                            ),
+                            DiffContentFactory.getInstance().create(
+                                session.generatedTestDiffs.values.first(),
+                                virtualFile
                             ),
-                            DiffContentFactory.getInstance().create(session.generatedTestDiffs.values.first()),
                             "Before",
                             "After"
                         )
                     )
+                    Files.deleteIfExists(tempPath)
                     session.openedDiffFile = FileEditorManager.getInstance(context.project).selectedEditor?.file
                     ApplicationManager.getApplication().runReadAction {
                         generatedFileContent = getGeneratedFileContent(session)