Clearer guidance on pytest.raise(match=...) failure (pytest-dev#7499)

(cherry picked from commit 71ab623)

AUTHORS

@@ -157,6 +157,7 @@ Kyle Altendorf
 Lawrence Mitchell
 Lee Kamentsky
 Lev Maximov
+Lewis Cowles
 Llandy Riveron Del Risco
 Loic Esteve
 Lukas Bednar

changelog/7489.improvement.rst

@@ -0,0 +1 @@
+The :func:`pytest.raises` function has a clearer error message when ``match`` equals the obtained string but is not a regex match. In this case it is suggested to escape the regex.

src/_pytest/_code/code.py

@@ -665,9 +665,10 @@ def match(self, regexp: "Union[str, Pattern]") -> "Literal[True]":
         If it doesn't match an `AssertionError` is raised.
         """
         __tracebackhide__ = True
-        assert re.search(
-            regexp, str(self.value)
-        ), "Pattern {!r} does not match {!r}".format(regexp, str(self.value))
+        msg = "Regex pattern {!r} does not match {!r}."
+        if regexp == str(self.value):
+            msg += " Did you mean to `re.escape()` the regex?"
+        assert re.search(regexp, str(self.value)), msg.format(regexp, str(self.value))
         # Return True to allow for "assert excinfo.match()".
         return True
 

testing/code/test_excinfo.py

@@ -412,7 +412,7 @@ def test_division_zero():
     result = testdir.runpytest()
     assert result.ret != 0
 
-    exc_msg = "Pattern '[[]123[]]+' does not match 'division by zero'"
+    exc_msg = "Regex pattern '[[]123[]]+' does not match 'division by zero'."
     result.stdout.fnmatch_lines(["E * AssertionError: {}".format(exc_msg)])
     result.stdout.no_fnmatch_line("*__tracebackhide__ = True*")
 

testing/python/raises.py

@@ -198,7 +198,7 @@ def test_raises_match(self) -> None:
             int("asdf")
 
         msg = "with base 16"
-        expr = "Pattern {!r} does not match \"invalid literal for int() with base 10: 'asdf'\"".format(
+        expr = "Regex pattern {!r} does not match \"invalid literal for int() with base 10: 'asdf'\".".format(
             msg
         )
         with pytest.raises(AssertionError, match=re.escape(expr)):
@@ -224,7 +224,19 @@ def test_match_failure_string_quoting(self):
             with pytest.raises(AssertionError, match="'foo"):
                 raise AssertionError("'bar")
         (msg,) = excinfo.value.args
-        assert msg == 'Pattern "\'foo" does not match "\'bar"'
+        assert msg == 'Regex pattern "\'foo" does not match "\'bar".'
+
+    def test_match_failure_exact_string_message(self):
+        message = "Oh here is a message with (42) numbers in parameters"
+        with pytest.raises(AssertionError) as excinfo:
+            with pytest.raises(AssertionError, match=message):
+                raise AssertionError(message)
+        (msg,) = excinfo.value.args
+        assert msg == (
+            "Regex pattern 'Oh here is a message with (42) numbers in "
+            "parameters' does not match 'Oh here is a message with (42) "
+            "numbers in parameters'. Did you mean to `re.escape()` the regex?"
+        )
 
     def test_raises_match_wrong_type(self):
         """Raising an exception with the wrong type and match= given.