Golang Testing Helper
Jul 6, 2022
Go t.Helper() makes it easy to report test failures at the call site of the parent function rather than the call site of t.(Error|Fatal). I’ve used stretchr/testify in a couple of projects but in general I’ve not been happy with the extensive use of interface{} in the API. It results in a lot of run-time failures that would otherwise be caught with proper types. Another minor quibble is that testify encouraged overwriting the assert import namespace with a local assert variable in it’s docs. With any solution I’d like to address both of those issues.
An Alternative
With a recent project I decided to write my own assertion library. I settled on the following API:
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assert.Int(t, actual).Equals(expected)
Under the hood it looks as follows:
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package assert
import "testing"
func Int(t *testing.T, i int) *integer {
return &integer{i, t}
}
type integer struct {
a int
t *testing.T
}
func (i *integer) Equals(b int) {
if i.a != b {
i.t.Errorf("want %v, got %v\n", b, i.a)
}
}
While fluent API’s aren’t considered idiomatic Go, I found them justified in this context. It helps narrow the scope of functions that can be applied to a given type. With IntelliSense it reduces my dependence on looking up docs and keeping focus on the code.
The gotcha
When I first implemented these functions I found test failures weren’t as helpful as inline conditional block checks. Enter the Helper() receiver function. This function rolls the stack to your tests call site rather than the helper call site. So all the trace data points to your helper and not the test. Adding t.Helper() solves that in one line:
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func (i *integer) Equals(b int) {
i.t.Helper()
if i.a != b {
i.t.Errorf("want %v, got %v\n", b, i.a)
}
}