Testing in Go

This weekend I wrote a bunch of “happy path” tests in Go.

I’ve been writing tests alongside my own software for a long time. When I started porting tools to Go I decided getting something that would function was higher priority than quality, including tests, documentation, and style. I think that was the right call, but I’ve been writing enough Go now that I’m circling back and at least writing basic tests so that if I come across some weird bug I can hack in a test to fix it.

Tests in Go are far less important than they are in, for example, Perl, where the lack of static typing necesarily means that compilation means less. Sure, perl -c is worth doing; you’ll at least find out if you misspelled a variable, but in Go the static types mean that, generally speaking, code that compiles, works.

I still like to at least have basic tests, if only because it allows me to iterate faster while implementing features. If you are building something that scrapes a webpage (which I do weirdly often) it’s probably better to make a test that starts with a copy-pasted version of the site you are scraping, rather than hitting the real thing every time. You will need to update your test when the real site changes, but it’s still nice to ensure that your test suite has examples of all the weird edge cases you’ve run into.

Part of the interesting thing here, to me, is that Go ships with a package specifically made for testing web applications. Perl’s de facto solution, on the other hand, is Test::TCP, which can be a bit flaky. I think the issue here is that Go has engineers being paid to work on the standard library who have leadership and momentum keeping the standard library of high quality.

Perl (and nearly all other Open Source languages, like Ruby, Python, PHP, etc) just depends on volunteers to make good choices. Frustrating stuff.

Here’s one of my tests that works well and I think shows off a couple neat features of Go’s test harness:

func TestLoadCoffee(t *testing.T) {
	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/html")
		f, err := os.Open("./sm.html")
		if err != nil {
		_, err = io.Copy(w, f)
		if err != nil {
	defer ts.Close()

	c, err := LoadCoffee(ts.URL)
	if err != nil {
		t.Fatalf("Failed to LoadCoffee: %s", err)

	assert.Equal(t, Coffee{
		Title:    "Papua New Guinea Honey Nebilyer Estate",
		Score:    86.6,
		URL:      ts.URL,

		// ...
	}, c)

The first cool thing you can see is the trivial creation of ts, a test http server that can serve content for the client I’m testing. Another convenience is that I can trivially load content from disk because when testing a package go test automatically runs the test harness in the package directory, where you can put various bits of test data.

This example isn’t even as good as it could get, but I’m trying to first increase coverage before adding various test cases. If you write Go and want to get better at testing, I strongly recommend watching Mitchell Hashimoto’s Advanced Testing with Go.

If you watch that talk you’ll see really powerful examples where, for example, in a single function he creates both a client and server socket for use in tests. This is something I would never have considered doing in any other language. Maybe it’s because in other languages people were more willing to just test protocols without the socket objects.

In any case I am inspired to try writing more tests with greater coverage for my Go.

I mentioned both of these books yesterday, but it bears repeating: if you want to learn Go or improve your testing in Go, both The Go Programming Language and Go Programming Blueprints are good options.

Posted Thu, Mar 28, 2019

If you're interested in being notified when new posts are published, you can subscribe here; you'll get an email once a week at the most.