This directory consists of snippets of gcode that should be rejected because
they are not valid.  All files that match the glob '*.ngc' are tested.
The first line should consist of a ";" followed by the exact English
error string that the interpreter should show.  This is followed
by zero or more lines of test gcode.

An individual file is considered to be a failure if
 * it is accepted by the interpreter
 * or the error message does not exactly match the specification

An individual file is considered to be bad if
 * it does not contain a parseable error specification
 * the error message cannot be isolated in the interpreter's output

If any file is a failure or is bad, then the test as a whole fails and will
count as 1 failure in the testsuite.