session/test_env_select: Split tests into direct and indirect groups

All but one of the tests in this test module are actually testing
env_select functionality through calling other code that in turn
uses env_select (CliEnv, EnvSelector and register_env_select_flags).

Split these into two groups so that this is more clear.

Author: 0cjs

tests/session/test_env_select.py

@@ -15,6 +15,21 @@
 
 CURRENT_PY_ENV = f"py{sys.version_info[0]}{sys.version_info[1]}"  # e.g. py310
 
+####################################################################
+#   Tests directly on env_select functionality.
+
+
+def test_env_select_lazily_looks_at_envs() -> None:
+    state = State(get_options(), [])
+    env_selector = EnvSelector(state)
+    # late-assigning env should be reflected in env_selector
+    state.conf.options.env = CliEnv("py")
+    assert set(env_selector.iter()) == {"py"}
+
+
+####################################################################
+#   Tests of env_select functionality as used through other code.
+
 
 def test_label_core_can_define(tox_project: ToxProjectCreator) -> None:
     ini = """
@@ -130,14 +145,6 @@ def test_tox_skip_env_logs(tox_project: ToxProjectCreator, monkeypatch: MonkeyPa
     outcome.assert_out_err("ROOT: skip environment mypy, matches filter 'm[y]py'\npy310\npy39\n", "")
 
 
-def test_env_select_lazily_looks_at_envs() -> None:
-    state = State(get_options(), [])
-    env_selector = EnvSelector(state)
-    # late-assigning env should be reflected in env_selector
-    state.conf.options.env = CliEnv("py")
-    assert set(env_selector.iter()) == {"py"}
-
-
 def test_cli_env_can_be_specified_in_default(tox_project: ToxProjectCreator) -> None:
     proj = tox_project({"tox.ini": "[tox]\nenv_list=exists"})
     outcome = proj.run("r", "-e", "exists")