Keep only unique overridden elements.

pkg/analysis_server/test/analysis/notification_overrides_test.dart

Index: pkg/analysis_server/test/analysis/notification_overrides_test.dart
diff --git a/pkg/analysis_server/test/analysis/notification_overrides_test.dart b/pkg/analysis_server/test/analysis/notification_overrides_test.dart
index 23393081e1c2cccf06e2c0bb60320248a51cbb9f..bd0343f5c557f352a246c8af53ddceeb902d0c0c 100644
--- a/pkg/analysis_server/test/analysis/notification_overrides_test.dart
+++ b/pkg/analysis_server/test/analysis/notification_overrides_test.dart
@@ -227,6 +227,58 @@ class C implements B {
     });
   }
 
+  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 {