Tests: create TestCase subclass with a permissions check assertion

The subclass will contain assertions that are useful for testing Discord
commands. The currently included assertion tests that a command will
raise a MissingPermissions exception if the author lacks permissions.

1 files changed, 34 insertions, 0 deletions

diff --git a/tests/base.py b/tests/base.py
index 029a249ed..88693f382 100644
--- a/tests/base.py
+++ b/tests/base.py
@@ -1,6 +1,12 @@
 import logging
 import unittest
 from contextlib import contextmanager
+from typing import Dict
+
+import discord
+from discord.ext import commands
+
+from tests import helpers
 
 
 class _CaptureLogHandler(logging.Handler):
@@ -65,3 +71,31 @@ class LoggingTestCase(unittest.TestCase):
             standard_message = self._truncateMessage(base_message, record_message)
             msg = self._formatMessage(msg, standard_message)
             self.fail(msg)
+
+
+class CommandTestCase(unittest.TestCase):
+    """TestCase with additional assertions that are useful for testing Discord commands."""
+
+    @helpers.async_test
+    async def assertHasPermissionsCheck(
+        self,
+        cmd: commands.Command,
+        permissions: Dict[str, bool],
+    ) -> None:
+        """
+        Test that `cmd` raises a `MissingPermissions` exception if author lacks `permissions`.
+
+        Every permission in `permissions` is expected to be reported as missing. In other words, do
+        not include permissions which should not raise an exception along with those which should.
+        """
+        # Invert permission values because it's more intuitive to pass to this assertion the same
+        # permissions as those given to the check decorator.
+        permissions = {k: not v for k, v in permissions.items()}
+
+        ctx = helpers.MockContext()
+        ctx.channel.permissions_for.return_value = discord.Permissions(**permissions)
+
+        with self.assertRaises(commands.MissingPermissions) as cm:
+            await cmd.can_run(ctx)
+
+        self.assertCountEqual(permissions.keys(), cm.exception.missing_perms)