Instead of returning an `error` from `processTestFile` for the result, use `t` inside of the runner:

```go
filepath.Walk(testResources, testFileRunner(t))
```
and then make `testFileRunner` return a closure closed over `t` (untested code):

```go
func testFileRunner(t *testing.T) func(string, os.FileInfo, error) error {
  return func(path string, _ os.FileInfo, err error) error {
    // run test file and use t.Error in here
  }
}