Use STDIN project in test_projects to ensure it runs quickly (#2575)

Existing test was actually running a full black-primer
run which could be slow. This goes from 8 seconds to
0.4 seconds on my machine.

Needed to move to top level scope to leverage the caplog
feature of pytest in order to test that the command line
was parsing the bogus arguments and dumping to stderr.

tests/test_primer.py

@@ -9,6 +9,7 @@
 from os import getpid
 from pathlib import Path
 from platform import system
+from pytest import LogCaptureFixture
 from subprocess import CalledProcessError
 from tempfile import TemporaryDirectory, gettempdir
 from typing import Any, Callable, Iterator, List, Tuple, TypeVar
@@ -267,18 +268,23 @@ def test_help_output(self) -> None:
         result = runner.invoke(cli.main, ["--help"])
         self.assertEqual(result.exit_code, 0)
 
-    def test_projects(self) -> None:
-        runner = CliRunner()
-        with event_loop():
-            result = runner.invoke(cli.main, ["--projects=tox,asdf"])
-            self.assertEqual(result.exit_code, 0)
-            assert "1 / 1 succeeded" in result.output
 
-        with event_loop():
-            runner = CliRunner()
-            result = runner.invoke(cli.main, ["--projects=tox,attrs"])
-            self.assertEqual(result.exit_code, 0)
-            assert "2 / 2 succeeded" in result.output
+def test_projects(caplog: LogCaptureFixture) -> None:
+    with event_loop():
+        runner = CliRunner()
+        result = runner.invoke(cli.main, ["--projects=STDIN,asdf"])
+        assert result.exit_code == 0
+        assert "1 / 1 succeeded" in result.output
+        assert "Projects not found: {'asdf'}" in caplog.text
+
+    caplog.clear()
+
+    with event_loop():
+        runner = CliRunner()
+        result = runner.invoke(cli.main, ["--projects=fdsa,STDIN"])
+        assert result.exit_code == 0
+        assert "1 / 1 succeeded" in result.output
+        assert "Projects not found: {'fdsa'}" in caplog.text
 
 
 if __name__ == "__main__":