Correct target of ADD_MISSING_REQUIRED_ARGUMENT fixes (flutter-intellij#788)

pkg/analysis_server/test/services/correction/fix_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.services.correction.fix;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
 import 'package:analysis_server/plugin/edit/fix/fix_dart.dart';
@@ skipping 59 matching lines @@
 main() {
   bool b = true;
   $lineWithTest
 }
 
 bool test() {
 }
 ''');
   }
 
-  assertHasFix(FixKind kind, String expected) async {
+  assertHasFix(FixKind kind, String expected, {String target}) async {
     AnalysisError error = await _findErrorToFix();
     fix = await _assertHasFix(kind, error);
     change = fix.change;
+
     // apply to "file"
     List<SourceFileEdit> fileEdits = change.edits;
     expect(fileEdits, hasLength(1));
+
+    if (target != null) {
+      expect(target, fileEdits.first.file);
+    }
+
     resultCode = SourceEdit.applySequence(testCode, change.edits[0].edits);
     // verify
     expect(resultCode, expected);
   }
 
   assertNoFix(FixKind kind) async {
     AnalysisError error = await _findErrorToFix();
     List<Fix> fixes = await _computeFixes(error);
     for (Fix fix in fixes) {
       if (fix.kind == kind) {
@@ skipping 325 matching lines @@
   test(int i) {}
   main() {
     test(1);
   }
 }
 ''');
   }
 
   test_addMissingRequiredArg_cons_single() async {
     _addMetaPackageSource();
-
-    await resolveTestUnit('''
+    addSource(
+        '/libA.dart',
+        r'''
+library libA;
 import 'package:meta/meta.dart';
 
 class A {
   A({@required int a}) {}
 }
+''');
+
+    await resolveTestUnit('''
+import 'libA.dart';
+
 main() {
   A a = new A();
 }
 ''');
     await assertHasFix(
         DartFixKind.ADD_MISSING_REQUIRED_ARGUMENT,
         '''
-import 'package:meta/meta.dart';
+import 'libA.dart';
 
-class A {
-  A({@required int a}) {}
-}
 main() {
   A a = new A(a: null);
 }
-''');
+''',
+        target: '/test.dart');
   }
 
   test_addMissingRequiredArg_multiple() async {
     _addMetaPackageSource();
 
     await resolveTestUnit('''
 import 'package:meta/meta.dart';
 
 test({@required int a, @required int bcd}) {}
 main() {
@@ skipping 5366 matching lines @@
 
   @override
   final CompilationUnit unit;
 
   @override
   final AnalysisError error;
 
   _DartFixContextImpl(this.resourceProvider, this.getTopLevelDeclarations,
       this.analysisContext, this.astProvider, this.unit, this.error);
 }