Error if @fail_slow is not given exactly one argument

CHANGELOG.md

@@ -1,3 +1,9 @@
+v0.3.0 (in development)
+-----------------------
+- The `@pytest.mark.fail_slow()` marker now errors if not given exactly one
+  argument.  Previously, it would either use the first argument or, if no
+  arguments were given, it would be ignored.
+
 v0.2.0 (2022-04-25)
 -------------------
 - Test against pytest 7

src/pytest_fail_slow.py

@@ -44,7 +44,7 @@
 Visit <https://github.com/jwodder/pytest-fail-slow> for more information.
 """
 
-__version__ = "0.2.0"
+__version__ = "0.3.0.dev1"
 __author__ = "John Thorvald Wodder II"
 __author_email__ = "pytest-fail-slow@varonathe.org"
 __license__ = "MIT"
@@ -109,7 +109,11 @@ def pytest_addoption(parser) -> None:
 def pytest_runtest_makereport(item, call):
     report = (yield).get_result()
     mark = item.get_closest_marker("fail_slow")
-    if mark is not None and len(mark.args) > 0:
+    if mark is not None:
+        if len(mark.args) != 1:
+            raise pytest.UsageError(
+                "@pytest.mark.fail_slow() takes exactly one argument"
+            )
         timeout = parse_duration(mark.args[0])
     else:
         timeout = item.config.getoption("--fail-slow")

test/test_fail_slow.py

@@ -99,3 +99,22 @@ def test_fail_slow_threshold(
         )
     else:
         result.stdout.no_fnmatch_line("*Test passed but took too long to run*")
+
+
+@pytest.mark.parametrize("args", ["", "42, 'foo'"])
+def test_fail_slow_marker_bad_args(pytester, args: str) -> None:
+    pytester.makepyfile(
+        test_func=(
+            "import pytest\n"
+            "\n"
+            f"@pytest.mark.fail_slow({args})\n"
+            "def test_func():\n"
+            "    assert 2 + 2 == 4\n"
+        )
+    )
+    result = pytester.runpytest()
+    result.assert_outcomes()
+    result.stdout.no_fnmatch_line("?")
+    result.stderr.fnmatch_lines(
+        ["ERROR: @pytest.mark.fail_slow() takes exactly one argument"]
+    )