Test session requires

nox/_decorators.py

@@ -120,7 +120,7 @@ def format_dependency(self, dependency: str) -> str:
                 msg = "Cannot parametrize requires with {python} when python is None or a bool."
                 raise ValueError(msg)
             return formatted
-        raise TypeError(
+        raise TypeError(  # pragma: no cover
             "The requires of a not-yet-parametrized session cannot be parametrized."
         )
 

tests/resources/noxfile_requires.py

@@ -0,0 +1,128 @@
+# Copyright 2022 Alethea Katherine Flowers
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import annotations
+
+import nox
+
+
+@nox.session(requires=["c", "b"])
+def a(session):
+    print(session.name)
+
+
+@nox.session()
+def b(session):
+    print(session.name)
+
+
+@nox.session()
+def c(session):
+    print(session.name)
+
+
+@nox.session(requires=["e"])
+def d(session):
+    print(session.name)
+
+
+@nox.session(requires=["c"])
+def e(session):
+    print(session.name)
+
+
+@nox.session(requires=["b", "g"])
+def f(session):
+    print(session.name)
+
+
+@nox.session(requires=["b", "h"])
+def g(session):
+    print(session.name)
+
+
+@nox.session(requires=["c"])
+def h(session):
+    print(session.name)
+
+
+#
+
+
+@nox.session(requires=["j"])
+def i(session):
+    print(session.name)
+
+
+@nox.session(requires=["i"])
+def j(session):
+    print(session.name)
+
+
+#
+
+
+@nox.session(python=["3.9", "3.10"])
+def k(session):
+    print(session.name)
+
+
+@nox.session(requires=["k"])
+def m(session):
+    print(session.name)
+
+
+@nox.session(python="3.10", requires=["k-{python}"])
+def n(session):
+    print(session.name)
+
+
+#
+
+
+@nox.session(requires=["does_not_exist"])
+def o(session):
+    print(session.name)
+
+
+#
+
+
+@nox.session(python=["3.9", "3.10"])
+def p(session):
+    print(session.name)
+
+
+@nox.session(python=None, requires=["p-{python}"])
+def q(session):
+    print(session.name)
+
+
+#
+
+
+@nox.session
+def r(session):
+    print(session.name)
+    raise Exception("Fail!")
+
+
+@nox.session(requires=["r"])
+def s(session):
+    print(session.name)
+
+
+@nox.session(requires=["r"])
+def t(session):
+    print(session.name)

tests/test_main.py

@@ -489,6 +489,56 @@ def test_main_with_bad_session_names(run_nox, session):
     assert session in stderr
 
 
+@pytest.mark.parametrize(
+    ("sessions", "expected_order"),
+    [
+        (("g", "a", "d"), ("b", "c", "h", "g", "a", "e", "d")),
+        (("m",), ("k-3.9", "k-3.10", "m")),
+        (("n",), ("k-3.10", "n")),
+    ],
+)
+def test_main_requires(run_nox, sessions, expected_order):
+    noxfile = os.path.join(RESOURCES, "noxfile_requires.py")
+    returncode, stdout, _ = run_nox(f"--noxfile={noxfile}", "--sessions", *sessions)
+    assert returncode == 0
+    assert tuple(stdout.rstrip("\n").split("\n")) == expected_order
+
+
+def test_main_requires_cycle(run_nox):
+    noxfile = os.path.join(RESOURCES, "noxfile_requires.py")
+    returncode, _, stderr = run_nox(f"--noxfile={noxfile}", "--session=i")
+    assert returncode != 0
+    # While the exact cycle reported is not unique and is an implementation detail, this
+    # still serves as a regression test for unexpected changes in the implementation's
+    # behavior.
+    assert "Sessions are in a dependency cycle: i -> j -> i" in stderr
+
+
+def test_main_requires_missing_session(run_nox):
+    noxfile = os.path.join(RESOURCES, "noxfile_requires.py")
+    returncode, _, stderr = run_nox(f"--noxfile={noxfile}", "--session=o")
+    assert returncode != 0
+    assert "Session not found: does_not_exist" in stderr
+
+
+def test_main_requires_bad_python_parametrization(run_nox):
+    noxfile = os.path.join(RESOURCES, "noxfile_requires.py")
+    with pytest.raises(
+        ValueError,
+        match="Cannot parametrize requires",
+    ):
+        returncode, _, _ = run_nox(f"--noxfile={noxfile}", "--session=q")
+        assert returncode != 0
+
+
+@pytest.mark.parametrize("session", ("s", "t"))
+def test_main_requires_chain_fail(run_nox, session):
+    noxfile = os.path.join(RESOURCES, "noxfile_requires.py")
+    returncode, _, stderr = run_nox(f"--noxfile={noxfile}", f"--session={session}")
+    assert returncode != 0
+    assert "Prerequisite session r was not successful" in stderr
+
+
 def test_main_noxfile_options(monkeypatch, generate_noxfile_options):
     noxfile_path = generate_noxfile_options(reuse_existing_virtualenvs=True)
     monkeypatch.setattr(