add tests to demonstrate missing generic function subtype logic

pkg/analyzer/test/src/task/strong/checker_test.dart

Index: pkg/analyzer/test/src/task/strong/checker_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/checker_test.dart b/pkg/analyzer/test/src/task/strong/checker_test.dart
index a1170ef89c78c06f4e35dec9b6aff2a07721aa80..1622cbc155e63b79162c038132ff9de0b818c4f1 100644
--- a/pkg/analyzer/test/src/task/strong/checker_test.dart
+++ b/pkg/analyzer/test/src/task/strong/checker_test.dart
@@ -247,7 +247,7 @@ void main() {
       class B extends A {
         B() : super(/*severe:STATIC_TYPE_ERROR*/"hello");
 
-        B.c2(int x, String y) : super.c2(/*severe:STATIC_TYPE_ERROR*/y, 
+        B.c2(int x, String y) : super.c2(/*severe:STATIC_TYPE_ERROR*/y,
                                          /*severe:STATIC_TYPE_ERROR*/x);
 
         B.c3(num x, Object y) : super.c3(x, /*info:DOWN_CAST_IMPLICIT*/y);
@@ -1351,6 +1351,51 @@ void main() {
        '''
   });
 
+  testChecker('generic class method override', {
+    '/main.dart': '''
+          class A {}
+          class B extends A {}
+
+          class Base<T extends B> {
+            T foo() => null;
+          }
+
+          class Derived<S extends A> extends Base<B> {
+            /*severe:INVALID_METHOD_OVERRIDE*/S foo() => null;
+          }
+
+          class Derived2<S extends B> extends Base<B> {
+            S foo() => null;
+          }
+       '''
+  });
+
+  testChecker('generic method override', {
+    '/main.dart': '''
+          class Future<T> {
+            /*=S*/ then/*<S>*/(/*=S*/ onValue(T t)) => null;
+          }
+
+          // These work because they're exactly equal FunctionTypes
+          class DerivedFuture<T> extends Future<T> {
+            /*=S*/ then/*<S>*/(/*=S*/ onValue(T t)) => null;
+          }
+
+          class DerivedFuture2<A> extends Future<A> {
+            /*=B*/ then/*<B>*/(/*=B*/ onValue(A a)) => null;
+          }
+
+          // These don't work but should.
+          class DerivedFuture3<T> extends Future<T> {
+            /*=/*severe:INVALID_METHOD_OVERRIDE should be pass*/S*/ then/*<S>*/(Object onValue(T t)) => null;
+          }
+
+          class DerivedFuture4<A> extends Future<A> {
+            /*=/*severe:INVALID_METHOD_OVERRIDE should be pass*/B*/ then/*<B>*/(Object onValue(A a)) => null;
+          }
+       '''
+  });
+
   testChecker('unary operators', {
     '/main.dart': '''
       class A {