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fix(gomock): display nil slices distinctly from empty slices in error messages #308

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fix(gomock): display nil slices distinctly from empty slices in error messages #308

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7 changes: 6 additions & 1 deletion gomock/call.go
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Original file line number Diff line number Diff line change
Expand Up @@ -498,7 +498,12 @@ func (c *Call) addAction(action func([]any) []any) {
}

func formatGottenArg(m Matcher, arg any) string {
got := fmt.Sprintf("%v (%T)", arg, arg)
var got string
if v := reflect.ValueOf(arg); v.Kind() == reflect.Slice && v.IsNil() {
got = fmt.Sprintf("nil (%T)", arg)
} else {
got = fmt.Sprintf("%v (%T)", arg, arg)
}
if gs, ok := m.(GotFormatter); ok {
got = gs.Got(arg)
}
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44 changes: 44 additions & 0 deletions gomock/controller_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,8 @@ func (s *Subject) ActOnTestStructMethod(arg TestStruct, arg1 int) int {

func (s *Subject) SetArgMethod(sliceArg []byte, ptrArg *int, mapArg map[any]any) {}
func (s *Subject) SetArgMethodInterface(sliceArg, ptrArg, mapArg any) {}
func (s *Subject) SliceArgMethod(arg []byte) {}
func (s *Subject) SliceOfArraysMethod(arg [][32]byte) {}

func assertEqual(t *testing.T, expected any, actual any) {
if !reflect.DeepEqual(expected, actual) {
Expand Down Expand Up @@ -622,6 +624,48 @@ func TestSetArgPtr(t *testing.T) {
}
}

func TestNilSliceVsEmptySlice(t *testing.T) {
reporter, ctrl := createFixtures(t)
defer reporter.recoverUnexpectedFatal()
subject := new(Subject)

ctrl.RecordCall(subject, "SliceArgMethod", []byte{})

var nilSlice []byte
reporter.assertFatal(func() {
// Calling with a nil slice should fail, but error message should clearly
// distinguish nil from empty slice (issue #69).
ctrl.Call(subject, "SliceArgMethod", nilSlice)
}, "Unexpected call to", "doesn't match the argument at index 0",
"Got: nil ([]uint8)\nWant: is equal to [] ([]uint8)")

reporter.assertFatal(func() {
// The expected call wasn't made.
ctrl.Finish()
})
}

func TestNilSliceOfArraysVsEmpty(t *testing.T) {
reporter, ctrl := createFixtures(t)
defer reporter.recoverUnexpectedFatal()
subject := new(Subject)

ctrl.RecordCall(subject, "SliceOfArraysMethod", [][32]byte{})

var nilSlice [][32]byte
reporter.assertFatal(func() {
// Reproduce the exact scenario from issue #69: nil vs empty [][32]byte.
// Before the fix, both would show as "[]" making them indistinguishable.
ctrl.Call(subject, "SliceOfArraysMethod", nilSlice)
}, "Unexpected call to", "doesn't match the argument at index 0",
"Got: nil ([][32]uint8)\nWant: is equal to [] ([][32]uint8)")

reporter.assertFatal(func() {
// The expected call wasn't made.
ctrl.Finish()
})
}

func TestReturn(t *testing.T) {
_, ctrl := createFixtures(t)
subject := new(Subject)
Expand Down