fail unit tests if coverage is below certain percentage

Question

I make a makefile that executes go test -cover. Is it possible to fail the make unit_tests command if coverage is below X? How would I do that?

Answer 1

You can use TestMain in your test to do that. TestMain can act as a custom entry point to tests, and then you can invoke testing.Coverage() to get access to the coverage stats.

So for example, if you want to fail at anything below 80%, you could add this to one of your package's test files:

func TestMain(m *testing.M) {
    // call flag.Parse() here if TestMain uses flags
    rc := m.Run()

    // rc 0 means we've passed, 
    // and CoverMode will be non empty if run with -cover
    if rc == 0 && testing.CoverMode() != "" {
        c := testing.Coverage()
        if c < 0.8 {
            fmt.Println("Tests passed but coverage failed at", c)
            rc = -1
        }
    }
    os.Exit(rc)
}

Then go test -cover will call this entry point and you'll fail:

PASS
coverage: 63.0% of statements
Tests passed but coverage failed at 0.5862068965517241
exit status 255
FAIL    github.com/xxxx/xxx 0.026s

Notice that the number that testing.Coverage() returns is lower than what the test reports. I've looked at the code and the function calculates its coverage differently than the test's internal reporting. I'm not sure which is more "correct".