Keep only unique overridden elements.

pkg/analysis_server/test/analysis/notification_overrides_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.analysis.notification.overrides;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/protocol.dart';
@@ skipping 209 matching lines @@
   m() {} // in C
 }
 ''');
     return prepareOverrides().then((_) {
       assertHasOverride('m() {} // in C');
       assertNoSuperMember();
       assertHasInterfaceMember('m() {} // in A');
     });
   }
 
+  test_interface_stopWhenFound() {
+    addTestFile('''
+class A {
+  m() {} // in A
+}
+class B extends A {
+  m() {} // in B
+}
+class C implements B {
+  m() {} // in C
+}
+''');
+    return prepareOverrides().then((_) {
+      assertHasOverride('m() {} // in C');
+      expect(override.interfaceMembers, hasLength(1));
+      assertHasInterfaceMember('m() {} // in B');
+    });
+  }
+
+  test_mix_sameMethod() {
+    addTestFile('''
+class A {
+  m() {} // in A
+}
+abstract class B extends A {
+}
+class C extends A implements A {
+  m() {} // in C
+}
+''');
+    return prepareOverrides().then((_) {
+      assertHasOverride('m() {} // in C');
+      assertHasSuperElement('m() {} // in A');
+      assertNoInterfaceMembers();
+    });
+  }
+
+  test_mix_sameMethod_Object_hashCode() {
+    addTestFile('''
+class A {}
+abstract class B {}
+class C extends A implements A {
+  int get hashCode => 42;
+}
+''');
+    return prepareOverrides().then((_) {
+      assertHasOverride('hashCode => 42;');
+      expect(override.superclassMember, isNotNull);
+      expect(override.interfaceMembers, isNull);
+    });
+  }
+
   test_staticMembers() {
     addTestFile('''
 class A {
   static int F = 0;
   static void M() {}
   static int get G => 0;
   static void set S(int v) {}
 }
 class B extends A {
   static int F = 0;
@@ skipping 161 matching lines @@
   set fff(x) {} // in B
 }
 ''');
     return prepareOverrides().then((_) {
       assertHasOverride('fff(x) {} // in B');
       assertHasSuperElement('fff(x) {} // in A');
       assertNoInterfaceMembers();
     });
   }
 }