mark more internal funcs as helpers

[gulducat]

hi!

given this test_test.go:

   1 package main
   2
   3 import (
   4     "testing"
   5
   6     "github.com/shoenig/test"
   7     "github.com/shoenig/test/must"
   8 )
   9
  10 func TestHelperStack(t *testing.T) {
  11     failSadly(t)
  12 }
  13
  14 func failSadly(t *testing.T) {
  15     t.Helper()
  16     test.NotNil(t, nil)
  17     must.NotNil(t, nil)
  18 }

before this change, error stack shows assert.go from this lib:

$ go test .
--- FAIL: TestHelperStack (0.00s)
    assert.go:14:
        test_test.go:16: expected to not be nil; is nil
    assert.go:14:
        test_test.go:17: expected to not be nil; is nil

after, shows my test file(s) with the context relevant to me and my terrible mistakes:

$ go test .
--- FAIL: TestHelperStack (0.00s)
    test_test.go:11:
        test_test.go:16: expected to not be nil; is nil
    test_test.go:11:
        test_test.go:17: expected to not be nil; is nil

[ccoVeille]

That's indeed t.Helper() purpose 👍

[shoenig]

LGTM, thanks @gulducat!