Prevent tests from producing dill files alongside the test file (#115075)

Fixes https://github.com/Dart-Code/Dart-Code/issues/4243.

packages/flutter_tools/lib/src/test/flutter_platform.dart

@@ -458,14 +458,16 @@ class FlutterPlatform extends PlatformPlugin {
         controllerSinkClosed = true;
       }));
 
-      // When start paused is specified, it means that the user is likely
-      // running this with a debugger attached. Initialize the resident
-      // compiler in this case.
-      if (debuggingOptions.startPaused) {
-        compiler ??= TestCompiler(debuggingOptions.buildInfo, flutterProject, precompiledDillPath: precompiledDillPath, testTimeRecorder: testTimeRecorder);
-        final Uri testUri = globals.fs.file(testPath).uri;
-        // Trigger a compilation to initialize the resident compiler.
-        unawaited(compiler!.compile(testUri));
+      void initializeExpressionCompiler(String path) {
+        // When start paused is specified, it means that the user is likely
+        // running this with a debugger attached. Initialize the resident
+        // compiler in this case.
+        if (debuggingOptions.startPaused) {
+          compiler ??= TestCompiler(debuggingOptions.buildInfo, flutterProject, precompiledDillPath: precompiledDillPath, testTimeRecorder: testTimeRecorder);
+          final Uri uri = globals.fs.file(path).uri;
+          // Trigger a compilation to initialize the resident compiler.
+          unawaited(compiler!.compile(uri));
+        }
       }
 
       // If a kernel file is given, then use that to launch the test.
@@ -474,6 +476,7 @@ class FlutterPlatform extends PlatformPlugin {
       String? mainDart;
       if (precompiledDillPath != null) {
         mainDart = precompiledDillPath;
+        initializeExpressionCompiler(testPath);
       } else if (precompiledDillFiles != null) {
         mainDart = precompiledDillFiles![testPath];
       } else {
@@ -489,6 +492,9 @@ class FlutterPlatform extends PlatformPlugin {
             testHarnessChannel.sink.addError('Compilation failed for testPath=$testPath');
             return null;
           }
+        } else {
+          // For integration tests, we may still need to set up expression compilation service.
+          initializeExpressionCompiler(mainDart);
         }
       }
 

packages/flutter_tools/test/integration.shard/expression_evaluation_test.dart

@@ -116,6 +116,12 @@ void batch2() {
     );
     await flutter.waitForPause();
     await evaluateTrivialExpressions(flutter);
+
+    // Ensure we did not leave a dill file alongside the test.
+    // https://github.com/Dart-Code/Dart-Code/issues/4243.
+    final String dillFilename = '${project.testFilePath}.dill';
+    expect(fileSystem.file(dillFilename).existsSync(), isFalse);
+
     await cleanProject();
   });
 
@@ -168,6 +174,12 @@ void batch3() {
     );
     await flutter.waitForPause();
     await evaluateTrivialExpressions(flutter);
+
+    // Ensure we did not leave a dill file alongside the test.
+    // https://github.com/Dart-Code/Dart-Code/issues/4243.
+    final String dillFilename = '${project.testFilePath}.dill';
+    expect(fileSystem.file(dillFilename).existsSync(), isFalse);
+
     await cleanProject();
   });