Hey! There's an issue I've been grappling with for ages - say I have a custom function, Print, that calls six other functions, FormatString, FormatBool, FormatXYZ, ..., and I have no tests. Once I write some basic tests for Print, it does call some of the other functions and from looking at my test coverage, it looks like I have those nested functions covered, but I never called them explicitly, I never did try all their corner cases, did not fuzz them or anything.
It may sound odd or not important, but I have encountered this in almost
every project in Go and other languages - the setup is always the same -
lots of small functions doing their thing and then some orchestrator that
integrates everything (could be a cli, could be an endpoint etc.) and once
I set that up, coverage spikes up.
Here's a simple example:
// calculator.go
package calculator
func Add(a, b int) int {
return a+b
}
func Calculator(a, b int) int {
return Add(a, b)
}
// calculator_test.go
package calculator
import "testing"
func TestCalculator(t *testing.T) {
s := Calculator(1, 2)
_ = s
}
In this case, Calculator is covered, and so is Add, but I never tested how
Add behaves for values close to the int maximum and with other potentially
dangerous edge cases.
I've though about this over the years a tiny bit and never really found a
great solution, because it's not really a technical thing, it's more about
the workflow and attitude to testing.
I prototyped a simple tool that looks up all the exported functions and
methods in a package and then checks if they are *explicitly* called in our
tests. This does not guarantee anything, but at least we know they were
explicitly used, not indirectly called within a different function. The
prototype does not quite work for methods, because I got kind of lost in
the go/{parser,ast} indirections. Also reassigning functions as first class
values and then calling them from a different variable will probably also
break it.
So it does give a lot of false positives for methods, but should be mostly
fine for functions.
While it probably does not solve any problems for any people apart from me,
I'll try and fix the method issues, because I do really need it for my own
test writing.
Do let me know if there's a better solution to this or if you've
encountered this and have some thoughts on the topic.
Thanks!
Ondrej
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