I wanted to add a possible use case here. In a table driven test, you might want to provide the number of times you expect a mocked method to be called. Sometimes, you may want a certain mocked method to not be called. In this case, you have to add an if statement in you test to check if the expected number of calls is >0, is so, setup your call assertions. A novel example:

package metricsmiddleware_test

import (
	"net/http"
	"net/http/httptest"
	"testing"
	"time"
	
	"github.com/mymodule/mocks"
)

func TestMetricsMiddleware(t *testing.T) {
	table := []struct {
		name             string
		status           int
		expectedLatency  time.Duration
		expected4XXCalls int
		expected5XXCalls int
	}{
		{
			name:             "it should send a latency metric with the expected duration",
			status:           200,
			expectedLatency:  time.Millisecond,
			expected4XXCalls: 0,
			expected5XXCalls: 0,
		},
		{
			name:             "it should send a 4xx error metric when the response status code is in the 400 range",
			status:           422,
			expectedLatency:  time.Millisecond,
			expected4XXCalls: 1,
			expected5XXCalls: 0,
		},
		{
			name:             "it should send a 5xx error metric when the response status code is in the 500 range",
			status:           500,
			expectedLatency:  time.Millisecond,
			expected4XXCalls: 1,
			expected5XXCalls: 0,
		},
	}

	for _, test := range table {
		t.Run(test.name, func(t *testing.T) {
			mockMetrics := &mocks.Metrics{}
			mockMetrics.On("Timing", "latency", test.expectedLatency, mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything).Return()
			mockMetrics.On("Incr", "error_4xx", mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything).Return().Times(test.expected4XXCalls)
			mockMetrics.On("Incr", "error_5xx", mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything, mock.Anything).Return().Times(test.expected5XXCalls)
			mockHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
				w.WriteHeader(test.status)
			})

			mw := middleware.NewMetricsMiddleware(mockMetrics)(mockHandler)
			mw.ServeHTTP(httptest.NewRecorder(), httptest.NewRequest("GET", "/foo", nil))

			mockMetrics.AssertExpectations(t)
		})
	}
}

The first test in the table won't pass with the current state, as 0 is passed to Times().

mock: add negative call expectations #566

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