Err returns only the last actual result of a multi-result function call, which typically is an error result.

NewTestWriter returns a new io.Writer which translates spaces into underscores and adornes new lines with a down-leftwards pointing arrow, and finally writing the result to a chained io.Writer.

PassFail runs a series of PASS and/or FAIL tests, checking for either success or the absence of success (failure might be to harsh a word).

FAIL expects a function under test to return an error.

TestWriter chains to another io.Writer and replaces certain characters as they pass through it for writing.

PASSFAIL is an expectation for a function to either return no error and thus PASS or to return an error and thus FAIL.

PASS is just another type of FAIL, after all.

PASSFAILS is a list of PASS and FAIL expectations for function calls returning errors.