1 files changed, 24 insertions, 0 deletions
diff --git a/tests/cli/llvmtestcase.py b/tests/cli/llvmtestcase.py
index 0f29ce6..f895c49 100644
--- a/tests/cli/llvmtestcase.py
+++ b/tests/cli/llvmtestcase.py
@@ -32,6 +32,30 @@ def debug(test):
     return wrapper
 
 
+def require_command_arg(requiredArg):
+    """
+    Decorator that simplifies writing CLI tests that check that 'requiredArg' is
+    in fact required (i.e. that the command that we're testing will blow up if
+    we don't pass it the required argument).
+
+    Use this to decorate test functions, e.g:
+
+    @require_command_arg("--my-required-arg")
+    def test_my_required_arg_is_compulsory(self):
+        run_command_without_my_required_arg()
+    """
+    def decorate(test):
+        def wrapper(*args, **kwargs):
+            self = args[0]
+            with self.assertRaises(subprocess.CalledProcessError) as context:
+                test(*args, **kwargs)
+
+            self.assertRegex(str(context.exception.output),
+                             "(.*\n)*the following arguments are required: {}(.*\n)*".format(requiredArg))
+        return wrapper
+    return decorate
+
+
 class LLVMTestCase(unittest.TestCase):
     python = "python3"
     script = os.path.join("scripts", "llvm.py")