assert.NoError have unexpected behavior

[MarioGravelAlithya]

Hi !
I just had issue with a custom made error struct because of a nil pointer.

If I use assert.NoError passing a nil pointer, it will fail. error being an interface, you should check for nil underlying values.
Here is the sandbox to explain the issue : https://go.dev/play/p/03adogriDwB

References : https://go.dev/tour/methods/12

Solution : in the file assertion.go, line #1381-1396

// NoError asserts that a function returned no error (i.e. `nil`).
//
//   actualObj, err := SomeFunction()
//   if assert.NoError(t, err) {
//	   assert.Equal(t, expectedObj, actualObj)
//   }
func NoError(t TestingT, err error, msgAndArgs ...interface{}) bool {
	if err != nil && !reflect.ValueOf(err).IsNil() {
		if h, ok := t.(tHelper); ok {
			h.Helper()
		}
		return Fail(t, fmt.Sprintf("Received unexpected error:\n%+v", err), msgAndArgs...)
	}

	return true
}

If you want me to open a pull-request for this quick fix, just let me know.

Thanks !

[brackendawson]

I'm not able to reproduce your problem: https://go.dev/play/p/V2YQ2_ozEKc

Can you share a minimal recreate?

[mario-gravel]

Here it is : https://go.dev/play/p/sciEHYfC7dv

Is the nil assignation is done to an interface variable, it's fine. But when the nil assignation is done to an object that fits the error interface, there is a problem. It is still nil, you can't call .Error() on it.

[mario-gravel]

This one better explain my point

https://go.dev/play/p/sX_e79lX2H7

Thanks for your time ! I appreciate.

[brackendawson]

Apologies if I've not understood you properly, I could really use an example of a test that fails but you expect to pass.

You are expecting a non-nil error that contains a nil pointer to indicate "no error", according to the specification that is not correct.

The panic when you call err.Error() is a bug in your custom error which can be fixed as the documentation you link to describes: https://go.dev/play/p/0jwANOfMIMG

[mario-gravel]

We both understand what's going on. I think there is two way of seeing it. As you said, and I agree, an interface pointing to a struct that is nil should not be equal to nil because it isn't. I was expecting assert.Nil to take care of this situation. About the NoError, I was expecting it to return false if there is no Error in the chain.

If you consider it right, I'm pretty fine with that and I thank you for your time and patience. My mindset is build on the way that I learned Go : If you are checking an interface{} for nil value, make sure you look at its value with reflect.ValueOf('interface').IsNil().

Thank you again and you may close this issue as you please.

[dolmen]

I agree with @brackendawson.

nil might be a valid value for some custom error types.

assert.NoError can't reject them even if it is an unusual practice.