pytest: Shorten traceback length by default

This produces a lot of code output which is not very helpful and is quite
annoying to wade through. Use the short format by default.

Signed-off-by: Simon Glass <sjg@chromium.org>

doc/develop/py_testing.rst

@@ -103,6 +103,13 @@ will be written to `${build_dir}/test-log.html`. This is best viewed in a web
 browser, but may be read directly as plain text, perhaps with the aid of the
 `html2text` utility.
 
+Controlling output
+~~~~~~~~~~~~~~~~~~
+
+By default a short backtrace is reported. If you would like a longer one,
+pass ``--tb=long`` when running the test. See the pytest documentation for
+more options.
+
 Running tests in parallel
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 

test/py/test.py

@@ -17,4 +17,9 @@ if __name__ == '__main__':
     # argv; py.test test_directory_name user-supplied-arguments
     args = [os.path.dirname(__file__) + '/tests']
     args.extend(sys.argv)
+
+    # Use short format by default
+    if not [arg for arg in args if '--tb=' in arg]:
+        args.append('--tb=short')
+
     sys.exit(pytest.main(args))