Fix empty error message when call is exhausted (#460)

Fixes #404

Author: cvgw

gomock/callset.go

@@ -84,7 +84,11 @@ func (cs callSet) FindMatch(receiver interface{}, method string, args []interfac
 	for _, call := range exhausted {
 		if err := call.matches(args); err != nil {
 			_, _ = fmt.Fprintf(&callsErrors, "\n%v", err)
+			continue
 		}
+		_, _ = fmt.Fprintf(
+			&callsErrors, "all expected calls for method %q have been exhausted", method,
+		)
 	}
 
 	if len(expected)+len(exhausted) == 0 {

gomock/callset_test.go

@@ -74,3 +74,26 @@ func TestCallSetRemove(t *testing.T) {
 		cs.Remove(c)
 	}
 }
+
+func TestCallSetFindMatch(t *testing.T) {
+	t.Run("call is exhausted", func(t *testing.T) {
+		cs := callSet{}
+		var receiver interface{} = "TestReceiver"
+		method := "TestMethod"
+		args := []interface{}{}
+
+		c1 := newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func))
+		cs.exhausted = map[callSetKey][]*Call{
+			callSetKey{receiver: receiver, fname: method}: []*Call{c1},
+		}
+
+		_, err := cs.FindMatch(receiver, method, args)
+		if err == nil {
+			t.Fatal("expected error, but was nil")
+		}
+
+		if err.Error() == "" {
+			t.Fatal("expected error to have message, but was empty")
+		}
+	})
+}