scripts: add spdxcheck.py self test

Add a script that will run spdxcheck.py through a couple of self tests to
simplify validation in the future.  The tests are run for both Python 2
and Python 3 to make sure all changes to the script remain compatible
across both versions.

The script tests a regular text file (Makefile) for basic sanity checks
and then runs it on a binary file (Documentation/logo.gif) to make sure it
works in both cases.  It also tests opening files passed on the command
line as well as piped files read from standard input.  Finally a run on
the complete tree will be performed to catch any other potential issues.

Link: http://lkml.kernel.org/r/20181212131210.28024-2-thierry.reding@gmail.comSigned-off-by: Thierry Reding <treding@nvidia.com>
Thomas Gleixner <tglx@linutronix.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Joe Perches <joe@perches.com>
Cc: Jeremy Cline <jcline@redhat.com>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/spdxcheck-test.sh

+#!/bin/sh
+
+for PYTHON in python2 python3; do
+	# run check on a text and a binary file
+	for FILE in Makefile Documentation/logo.gif; do
+		$PYTHON scripts/spdxcheck.py $FILE
+		$PYTHON scripts/spdxcheck.py - < $FILE
+	done
+
+	# run check on complete tree to catch any other issues
+	$PYTHON scripts/spdxcheck.py > /dev/null
+done