Workaround race condition in printing of diff values.

mock/mock.go

@@ -886,15 +886,15 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 			actualFmt = "(Missing)"
 		} else {
 			actual = objects[i]
-			actualFmt = fmt.Sprintf("(%[1]T=%[1]v)", actual)
+			actualFmt = fmt.Sprintf("(%[1]T=%[1]p)", actual)
 		}
 
 		if len(args) <= i {
 			expected = "(Missing)"
 			expectedFmt = "(Missing)"
 		} else {
 			expected = args[i]
-			expectedFmt = fmt.Sprintf("(%[1]T=%[1]v)", expected)
+			expectedFmt = fmt.Sprintf("(%[1]T=%[1]p)", expected)
 		}
 
 		if matcher, ok := expected.(argumentMatcher); ok {

mock/mock_test.go

@@ -1847,6 +1847,41 @@ func Test_MockReturnAndCalledConcurrent(t *testing.T) {
 	wg.Wait()
 }
 
+// Test to validate fix for racy concurrent value access in MethodCalled()
+func Test_MockRunAndCalledConcurrent(t *testing.T) {
+	type argType struct {
+		Value int
+	}
+
+	arg := argType{}
+
+	iterations := 1000
+	m := &Mock{}
+	call := m.On("ConcurrencyTestMethod", Anything)
+
+	wg := sync.WaitGroup{}
+	wg.Add(2)
+
+	go func() {
+		for i := 0; i < iterations; i++ {
+			call.Run(func(args Arguments) {
+				u := args.Get(2).(*argType)
+				// u.mu.Lock()
+				u.Value = 2
+				// u.mu.Unlock()
+			})
+		}
+		wg.Done()
+	}()
+	go func() {
+		for i := 0; i < iterations; i++ {
+			m.Called(arg)
+		}
+		wg.Done()
+	}()
+	wg.Wait()
+}
+
 type timer struct{ Mock }
 
 func (s *timer) GetTime(i int) string {