Mark multiple extras as not supported yet

pyproject_buildrequires.py

@@ -212,8 +212,10 @@ def main(argv):
     )
     parser.add_argument(
         '-x', '--extras', metavar='EXTRAS', default='',
-        help='comma separated list of "extras" for runtime requirements '
+        help='extra for runtime requirements (e.g. -x testing)',
-            + '(e.g. -x testing,feature-x)',
+        # XXX: a comma-separated list should be possible here
+        #help='comma separated list of "extras" for runtime requirements '
+        #    + '(e.g. -x testing,feature-x)',
     )
 
     args = parser.parse_args(argv)

test_pyproject_buildrequires.py

@@ -19,6 +19,9 @@ def test_data(case_name, capsys, tmp_path, monkeypatch):
     cwd.mkdir()
     monkeypatch.chdir(cwd)
 
+    if case.get('xfail'):
+        pytest.xfail(case.get('xfail'))
+
     if 'pyproject.toml' in case:
         cwd.joinpath('pyproject.toml').write_text(case['pyproject.toml'])
 

testcases.yaml

@@ -224,3 +224,31 @@ Run dependencies with extras (selected):
     python3dist(nose)
     python3dist(requests)
   result: 0
+
+Run dependencies with multiple extras:
+  xfail: requirement.marker.evaluate seems to not support multiple extras
+  freeze_output: |
+    setuptools==50
+    wheel==1
+    pyyaml==1
+  include_runtime: true
+  extras: testing,more-testing, even-more-testing , cool-feature
+  setup.py: |
+    from setuptools import setup
+    setup(
+        extras_require={
+            'testing': ['dep1'],
+            'more-testing': ['dep2'],
+            'even-more-testing': ['dep3'],
+            'cool-feature': ['dep4'],
+        },
+    )
+  expected: |
+    python3dist(setuptools) >= 40.8
+    python3dist(wheel)
+    python3dist(wheel)
+    python3dist(dep1)
+    python3dist(dep2)
+    python3dist(dep3)
+    python3dist(dep4)
+  result: 0