Show equivalent pytest command (#6363)

This is just a quick change to help users trouble-shoot problems with pytest. When there is a failure, we print out the command they can run at the shell to duplicate the error.

pythonFiles/testing_tools/adapter/pytest/_discovery.py

@@ -28,11 +28,15 @@ def discover(pytestargs=None, hidestdio=False,
         # No tests were discovered.
         pass
     elif ec != 0:
+        print(('equivalent command: {} -m pytest {}'
+               ).format(sys.executable, util.shlex_unsplit(pytestargs)))
         if hidestdio:
             print(stdio.getvalue(), file=sys.stderr)
             sys.stdout.flush()
         raise Exception('pytest discovery failed (exit code {})'.format(ec))
     if not _plugin._started:
+        print(('equivalent command: {} -m pytest {}'
+               ).format(sys.executable, util.shlex_unsplit(pytestargs)))
         if hidestdio:
             print(stdio.getvalue(), file=sys.stderr)
             sys.stdout.flush()

pythonFiles/testing_tools/adapter/util.py

@@ -59,3 +59,34 @@ def group_attr_names(attrnames):
             group = 'other'
         grouped[group].append(name)
     return grouped
+
+
+def shlex_unsplit(argv):
+    """Return the shell-safe string for the given arguments.
+
+    This effectively the equivalent of reversing shlex.split().
+    """
+    argv = [_quote_arg(a) for a in argv]
+    return ' '.join(argv)
+
+
+try:
+    from shlex import quote as _quote_arg
+except ImportError:
+    def _quote_arg(arg):
+        parts = None
+        for i, c in enumerate(arg):
+            if c.isspace():
+                pass
+            elif c == '"':
+                pass
+            elif c == "'":
+                c = "'\"'\"'"
+            else:
+                continue
+            if parts is None:
+                parts = list(arg)
+            parts[i] = c
+        if parts is not None:
+            arg = "'" + ''.join(parts) + "'"
+        return arg

pythonFiles/tests/testing_tools/adapter/test_util.py

@@ -0,0 +1,59 @@
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+
+import shlex
+import unittest
+
+from testing_tools.adapter.util import shlex_unsplit
+
+
+class ShlexUnsplitTests(unittest.TestCase):
+
+    def test_no_args(self):
+        argv = []
+        joined = shlex_unsplit(argv)
+
+        self.assertEqual(joined, '')
+        self.assertEqual(shlex.split(joined), argv)
+
+    def test_one_arg(self):
+        argv = ['spam']
+        joined = shlex_unsplit(argv)
+
+        self.assertEqual(joined, 'spam')
+        self.assertEqual(shlex.split(joined), argv)
+
+    def test_multiple_args(self):
+        argv = [
+                '-x', 'X',
+                '-xyz',
+                'spam',
+                'eggs',
+                ]
+        joined = shlex_unsplit(argv)
+
+        self.assertEqual(joined, '-x X -xyz spam eggs')
+        self.assertEqual(shlex.split(joined), argv)
+
+    def test_whitespace(self):
+        argv = [
+                '-x', 'X Y Z',
+                'spam spam\tspam',
+                'eggs',
+                ]
+        joined = shlex_unsplit(argv)
+
+        self.assertEqual(joined, "-x 'X Y Z' 'spam spam\tspam' eggs")
+        self.assertEqual(shlex.split(joined), argv)
+
+    def test_quotation_marks(self):
+        argv = [
+                '-x', "'<quoted>'",
+                'spam"spam"spam',
+                "ham'ham'ham",
+                'eggs',
+                ]
+        joined = shlex_unsplit(argv)
+
+        self.assertEqual(joined, "-x ''\"'\"'<quoted>'\"'\"'' 'spam\"spam\"spam' 'ham'\"'\"'ham'\"'\"'ham' eggs")
+        self.assertEqual(shlex.split(joined), argv)