Add test for error on old-style metadata

Author: takluyver

flit_core/tests_core/samples/module1-old-metadata.toml

@@ -0,0 +1,13 @@
+[build-system]
+requires = ["flit_core >=3.2,<4"]
+build-backend = "flit_core.buildapi"
+
+[tool.flit.metadata]
+module = "module1"
+author = "Sir Robin"
+author-email = "[email protected]"
+home-page = "http://github.com/sirrobin/module1"
+description-file = "EG_README.rst"
+
+[tool.flit.metadata.urls]
+Documentation = "https://example.com/module1"

flit_core/tests_core/samples/module1-pkg.ini

@@ -386,3 +386,8 @@ def test_pep621_license_files(proj_license_files, files):
     proj.update(proj_license_files)
     info = config.read_pep621_metadata(proj, samples_dir / 'pep621_license_files' / 'pyproject.toml')
     assert info.metadata['license_files'] == files
+
+
+def test_old_style_metadata():
+    with pytest.raises(config.ConfigError, match=re.escape("[tool.flit.metadata]")):
+        config.read_flit_config(samples_dir / 'module1-old-metadata.toml')