Add test failure with descriptive error message when running tests without a {project} placeholder

test/test_testing.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import os
 import subprocess
 import textwrap
+from pathlib import Path
 
 import pytest
 
@@ -151,3 +152,29 @@ def test_failing_test(tmp_path):
         )
 
     assert len(os.listdir(output_dir)) == 0
+
+
+def test_bare_pytest_invocation(tmp_path: Path, capfd: pytest.CaptureFixture[str]):
+    """Check that if a user runs pytest in the the test cwd, it raises a helpful error"""
+    project_dir = tmp_path / "project"
+    output_dir = tmp_path / "output"
+    project_with_a_test.generate(project_dir)
+
+    with pytest.raises(subprocess.CalledProcessError):
+        utils.cibuildwheel_run(
+            project_dir,
+            output_dir=output_dir,
+            add_env={
+                "CIBW_TEST_REQUIRES": "pytest",
+                "CIBW_TEST_COMMAND": "python -m pytest",
+            },
+        )
+
+    assert len(os.listdir(output_dir)) == 0
+
+    captured = capfd.readouterr()
+
+    assert (
+        "Please specify a path to your tests when invoking pytest using the {project} placeholder"
+        in captured.out
+    )