mock.AnythingOfType fix panic when matching nil type

[brackendawson]

Fix a panic in the AnythingOfType matcher when matching nil type.

It's reported that IsType had the same panic but a refactor between then and now appears to have fixed this.

Summary

Changes

• Handle the nil type case before calling reflect.Type.String.
• Because (=) looks confusing, change the failure message value format to the more idiomatic (%T)(%v).
• In order to better test the failure message, change the mockTestingT to capture the messages passed to it.

Motivation

AnythingOfType would panic if the actual arg value was of type nil.

Related issues

• Closes Mock panics when argument of nil type checked against AnythingOfType #1209
• Supersedes Nil actual type made AnythingOfType matcher panic #1219

[ccoVeille]

This format seems awkward to me.

I feel like we are using something like this everywhere else

Suggested change

	assert.Contains(t, diff, `(int)(456) != (int)(123)`)
	assert.Contains(t, diff, `(string)(false) != (bool)(true)`)
	assert.Contains(t, diff, `456(int) != 123(int)`)
	assert.Contains(t, diff, `false(string) != true(bool)`)

[ccoVeille]

Think about something storing "bool" in a string. The result is confusing

[brackendawson]

(string)(false) is a bit confusing. However *int(1) is also confusing because it's invalid in go. I'm going to restore the original format.

[ccoVeille]

I'm a bit lost there

I was suggesting to use "false (string)"

I felt like it was better than "(false)(string)"

So the example of "*int(1)" is incorrect. I was asking to use "1 (*int)" (even if I'm unsure this format exists as you said)

My point was to use something like "%v (%T)" that we are already using. And fix the strange format that exists in code for this method.

[brackendawson]

I mis-read your suggestion, %v(%T) is also quite weird to me because I was hoping to find something with a grounding in Go syntax.

This probably warrants de-coupling into a separate issue where we can consider the format we want testify to move to as a whole. As I said for now this PR just fixes the panic and leaves the format alone.