golang-table-tests-with-testify-mock

This repo shows how to test and mock multiple dependencies using table-driven tests with testify-mock in Golang

Problem

In unit testing and mocking world we need to mock multiple dependencies for specific test cases, (e.g) imagine we have a struct MacBook and it depends on CPU, GPU and RAM and we have a Diagnose method that returns an error if some of the dependencies used resources hits the threshold.

type MacBook struct {
	cpu    cpu.CPU
	gpu    gpu.GPU
	memory memory.RAM
}

func (m *MacBook) Diagnose(cpuThreshold, gpuThreshold, memoryThreshold int) error {
	if (m.cpu.Usage()) > cpuThreshold {
		return CpuUtilizationError
	}

	if m.gpu.Usage() > gpuThreshold {
		return GpuUsageError
	}

	if m.memory.FreeMemory() <= memoryThreshold {
		return MemoryUsageError
	}

	return nil
}

example above we have 3 if conditions, in order to test and get happy result that returns no error, we should have to write at least 4 unit tests or more and mock all dependencies.

Solution

func TestMacbookDiagnose(t *testing.T) {
	type depFields struct {
		cpu    *mockedCPU
		gpu    *mockedGPU
		memory *mockedRAM
	}

	type args struct {
		cpuThreshold, gpuThreshold, memoryThreshold int
	}

	tests := []struct {
		name string
		in   *args
		out  error

		on     func(*depFields)
		assert func(*depFields)
	}{
	
	 	// Test cases...
		
	 	{
			name: "when all thresholds not hit return nil",
			in:   &args{50, 90, 1000},
			out:  nil,
			on: func(df *depFields) {
				df.cpu.On("Usage").Return(40)           // 40% CPU usage less than cpuThreshold
				df.gpu.On("Usage").Return(50)           // 50% gpu usage less than gpuThreshold
				df.memory.On("FreeMemory").Return(2000) // 2000 MB free memory left so it is larger than 1000 mb threshold
			},
			assert: func(t *testing.T, df *depFields) {
				df.cpu.AssertNumberOfCalls(t, "Usage", 1)
				df.gpu.AssertNumberOfCalls(t, "Usage", 1)
				df.memory.AssertNumberOfCalls(t, "FreeMemory", 1)
			},
		},
	}

basically in the table-driven testing we will define slice of structs that represents test cases, in the example above we have struct that contains callback functions on: func(*depFields) and assert: func(*testing.T, *depFields) when we call those methods type depFields struct{} will be passed into it in order to mock or assert

for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			// arrange
			f := &depFields{
				&mockedCPU{},
				&mockedGPU{},
				&mockedRAM{},
			}
			mb := NewMacBook(f.cpu, f.gpu, f.memory)
			if tt.on != nil {
				tt.on(f)
			}
			// act
			err := mb.Diagnose(tt.in.cpuThreshold, tt.in.gpuThreshold, tt.in.memoryThreshold)

			// assert
			if err != tt.out {
				t.Errorf("got %v, want %v", err, tt.out)
			}
			if tt.assert != nil {
				tt.assert(t, f)
			}
		})
	}

example above we are iterating all test cases and running sub tests, on each case we creating f := &depFields{} of mocks and passing it onto on function to prepare mocks, at the end of the test we also checking assertion of mock calls, this helps us to assert number of calls that mocked methods are called inside the Diagnose method.

Links to read

Table-Driven tests in Go

Testify Mocking