Add unit tests to test for exception message contents; enhanced pypar…

…sing.testing.assertRaisesParseException to accept an expected exception message

CHANGES

@@ -18,6 +18,11 @@ Version 3.1.2 - in development
 - Updated pep8 synonym wrappers for better type checking compatibility. PR submitted
   by Ricardo Coccioli.
 
+- Fixed empty error message bug, PR submitted by InSync (#534).
+
+- Added unit tests to test for exception message contents, with enhancement to
+  pyparsing.testing.assertRaisesParseException to accept an expected exception message.
+
 - Some code refactoring to reduce code nesting, PRs submitted by InSync.
 
 

pyparsing/testing.py

@@ -1,8 +1,10 @@
 # testing.py
 
 from contextlib import contextmanager
+import re
 import typing
 
+
 from .core import (
     ParserElement,
     ParseException,
@@ -233,9 +235,16 @@ def assertRunTestResults(
             )
 
         @contextmanager
-        def assertRaisesParseException(self, exc_type=ParseException, msg=None):
-            with self.assertRaises(exc_type, msg=msg):
-                yield
+        def assertRaisesParseException(self, exc_type=ParseException, expected_msg=None, msg=None):
+            if expected_msg is not None:
+                if isinstance(expected_msg, str):
+                    expected_msg = re.escape(expected_msg)
+                with self.assertRaisesRegex(exc_type, expected_msg, msg=msg):
+                    yield
+
+            else:
+                with self.assertRaises(exc_type, msg=msg):
+                    yield
 
     @staticmethod
     def with_line_numbers(

tests/test_unit.py

@@ -10131,6 +10131,52 @@ def testForwardsDoProperStreamlining(self):
         self.assertEqual(len(ff.expr.exprs), 4)
         self.assertEqual(len(w3.exprs), 3)
 
+    test_exception_messages_tests = (
+        (
+            pp.Word(pp.alphas),
+            "123",
+            "Expected W:(A-Za-z), found '123'"
+        ),
+        (
+            pp.Word(pp.alphas).set_name("word"),
+            "123",
+            "Expected word, found '123'"
+        ),
+        (
+            pp.Group(pp.Word(pp.alphas).set_name("word")),
+            "123",
+            "Expected word, found '123'"
+        ),
+        (
+            pp.OneOrMore(pp.Word(pp.alphas).set_name("word")),
+            "123",
+            "Expected word, found '123'"
+        ),
+        (
+            pp.DelimitedList(pp.Word(pp.alphas).set_name("word")),
+            "123",
+            "Expected word, found '123'"
+        ),
+        (
+            pp.Suppress(pp.Word(pp.alphas).set_name("word")),
+            "123",
+            "Expected word, found '123'"
+        ),
+        (
+            pp.Forward() << pp.Word(pp.alphas).set_name("word"),
+            "123",
+            "Expected word, found '123'"
+        ),
+    )
+
+    def test_exception_messages(self, tests=test_exception_messages_tests):
+        for expr, input_str, expected_msg in tests:
+            with self.subTest(expr=expr, input_str=input_str):
+                with self.assertRaisesParseException(
+                        expected_msg=expected_msg
+                ):
+                    expr.parse_string(input_str)
+
 
 class Test03_EnablePackratParsing(TestCase):
     def runTest(self):