Golang testing — gotest.tools golden

Published on Sep 06, 2018 by Vincent Demeester.


Let’s continue the gotest.tools serie, this time with the golden package. This is a quick follow-up on a previous golden post, but focused on the gotest.tools implementation. I’m gonna be quicker, please read that one if golden files is a new concept for you.

Package golden provides tools for comparing large mutli-line strings.

Golden files are files in the ./testdata/ sub-directory of the package under test.

In the previous article, we described the problem, and how to fix it by writing a small helper. Well, that small helper is in gotest.tools/golden now, and it has a tiny bit more features.

One of the difference between the gotest.tools implementation and the previous post is the flag name. In gotest.tools/golden, the flag is -test.update-golden (was just -test.update before). Just as before, if the -test.update-golden flag is set then the actual content is written to the golden file, before reading it and comparing.

There is two ways to use the golden package:

  • on it’s own, using golden.Assert or golden.AssertBytes
  • as a cmp.Comparison, with golden.String or golden.Bytes

Assert and AssertBytes

Using Assert functions should be straightforward. Both Assert function compares the actual content to the expected content in the golden file and returns whether the assertion was successful (true) or not (false).

  • Assert uses string. Note that this one removes carriage return before comparing to depend as less as possible of the system (\n vs \r\n 😅)
  • AssertBytes uses raw data (in the form of []byte)
golden.Assert(t, "foo", "foo-content.golden")
// Could also be used to check some binary format
golden.AssertBytes(t, []byte("foo"), "foo-content.golden")

Bytes and String

As written in a previous post (about the assert package), I prefer to use cmp.Comparison.

All those helper functions have a equivalent function in the cmp package that returns a Comparison. I, personally, prefer to use assert.Check or assert.Assert in combination with cmp.Comparison as it allows me to write all my assertions the same way, with built-ins comparison or with my own — i.e. assert.Assert(t, is.Equal(…), "message" or assert.Assert(t, stackIsUp(c, time…), "another message").

The golden package gives us that too, in the form of Bytes and String. Using the assert.Check or assert.Assert functions with those is equivalent to their helper counter-part golden.Assert and golden.AssertBytes.

assert.Assert(t, golden.String("foo", "foo-content.golden"))
// Could also be used to check some binary format
assert.Assert(t, golden.Bytes([]byte("foo"), "foo-content.golden"))


… that’s a wrap. As for skip, this is a small package, so the post was going to be quick. golden package just solve a specific problem (read Golang testing — golden file) in a simple way.