Parallelize your table-driven tests

Tue, Sep 6, 2016

With Go 1.7, testing package supports sub-tests that allows you to run multiple smaller tests from a test case. Each sub test is reported independently in the go test output. More information about these recent additions can be found at Marcel van Lohuizen’s recent talk from GolangUK 2016.

These additions to Go 1.7 enabled reporting and other testing.T functionality for subtests. One of the biggest contributions of the recent changes is to be able to use these features for table-driven tests.

The other important feature it enables is to be able to parallelize the subtests (where makes sense) by using (*testing.T).Parallel().

func TestFoo(t *testing.T) {
	tc := []struct {
		dur time.Duration
	}{
		{time.Second},
		{2 * time.Second},
		{3 * time.Second},
		{4 * time.Second},
	}
	for _, tt := range tc {
		tt := tt
		t.Run("", func(st *testing.T) {
			st.Parallel()
			time.Sleep(tt.dur)
		})
	}
}

The test suite above will run roughly in 4 seconds rather than 10 seconds. TestFoo#01, TestFoo#02, TestFoo#03 and TestFoo#04 will begin at the same time, will wait for tt.dur and be completed.

$ go test -v
=== RUN   TestFoo
=== RUN   TestFoo/#00
=== RUN   TestFoo/#01
=== RUN   TestFoo/#02
=== RUN   TestFoo/#03
--- PASS: TestFoo (0.00s)
    --- PASS: TestFoo/#00 (1.00s)
    --- PASS: TestFoo/#01 (2.00s)
    --- PASS: TestFoo/#02 (3.00s)
    --- PASS: TestFoo/#03 (4.00s)
PASS
ok  	hello/subtests	4.020s

If you have table driven that are free from races and are majorly blocked by anything other than your CPU, consider parallelizing them with the new sub tests.

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Parallelize your table-driven tests