fix: Possible IndexError when a user-defined check raises an except…

…ion without a message

docs/changelog.rst

@@ -12,6 +12,11 @@ Changed
 - Hide ``Case.endpoint`` from representation. Its representation decreases the usability of pytest's output. `#719`_
 - Return registered functions from ``register_target`` and ``register_check`` decorators. `#721`_
 
+Fixed
+~~~~~
+
+- Possible ``IndexError`` when a user-defined check raises an exception without a message. `#718`_
+
 `2.4.0`_ - 2020-09-15
 ---------------------
 
@@ -1341,6 +1346,7 @@ Fixed
 
 .. _#721: https://github.com/schemathesis/schemathesis/issues/721
 .. _#719: https://github.com/schemathesis/schemathesis/issues/719
+.. _#718: https://github.com/schemathesis/schemathesis/issues/718
 .. _#708: https://github.com/schemathesis/schemathesis/issues/708
 .. _#705: https://github.com/schemathesis/schemathesis/issues/705
 .. _#692: https://github.com/schemathesis/schemathesis/issues/692

src/schemathesis/runner/impl/core.py

@@ -226,8 +226,12 @@ def run_checks(case: Case, checks: Iterable[CheckFunction], result: TestResult,
             if not skip_check:
                 result.add_success(check_name, case)
         except AssertionError as exc:
+            message = str(exc)
+            if not message:
+                message = f"Check '{check_name}' failed"
+                exc.args = (message,)
             errors.append(exc)
-            result.add_failure(check_name, case, str(exc))
+            result.add_failure(check_name, case, message)
 
     if errors:
         raise get_grouped_exception(*errors)

test/cli/test_commands.py

@@ -1002,18 +1002,24 @@ def reset_hooks():
     reset_checks()
 
 
-@pytest.fixture()
-def new_check(testdir, cli):
+@pytest.fixture(
+    params=[
+        ('AssertionError("Custom check failed!")', "1. Custom check failed!"),
+        ("AssertionError", "1. Check 'new_check' failed"),
+    ]
+)
+def new_check(request, testdir, cli):
+    exception, message = request.param
     module = testdir.make_importable_pyfile(
-        hook="""
+        hook=f"""
             import schemathesis
 
             @schemathesis.register_check
             def new_check(response, result):
-                raise AssertionError("Custom check failed!")
+                raise {exception}
             """
     )
-    yield module
+    yield module, message
     reset_checks()
     # To verify that "new_check" is unregistered
     result = cli.run("--help")
@@ -1026,6 +1032,7 @@ def new_check(response, result):
 
 @pytest.mark.endpoints("success")
 def test_register_check(new_check, cli, schema_url):
+    new_check, message = new_check
     # When `--pre-run` hook is passed to the CLI call
     # And it contains registering a new check, which always fails for the testing purposes
     result = cli.main("--pre-run", new_check.purebasename, "run", "-c", "new_check", schema_url)
@@ -1034,7 +1041,7 @@ def test_register_check(new_check, cli, schema_url):
     assert result.exit_code == ExitCode.TESTS_FAILED, result.stdout
     # And a message from the new check should be displayed
     lines = result.stdout.strip().split("\n")
-    assert lines[14] == "1. Custom check failed!"
+    assert lines[14] == message
 
 
 def assert_threaded_executor_interruption(lines, expected, optional_interrupt=False):