session/test_env_select: Reverse-engineer CliEnv and add tests for it

Some of the behaviour here, such as treatment of zero-length environment
names specified by the user, is not really intentional, but apparently an
artifact of the method used to parse the environment name list supplied by
the user.

Author: 0cjs

tests/session/test_env_select.py

@@ -16,6 +16,41 @@
 CURRENT_PY_ENV = f"py{sys.version_info[0]}{sys.version_info[1]}"  # e.g. py310
 
 
+@pytest.mark.parametrize(
+    ("user_input",      "env_names",            "is_all",   "is_default" ), [
+    (None,              (),                     False,      True         ),
+    ("",                (),                     False,      True         ),
+    ("a1",              ("a1",),                False,      False        ),
+    ("a1,b2,c3",        ("a1", "b2", "c3"),     False,      False        ),
+    #   If the user gives "ALL" as any envname, this becomes an "is_all" and other envnames are ignored.
+    ("ALL",             (),                     True,       False        ),
+    ("a1,ALL,b2",       (),                     True,       False        ),
+    #   Zero-length envnames are ignored as being not present. This is not intentional.
+    (",,a1,,,b2,,",     ("a1", "b2"),           False,      False        ),
+    (",,",              (),                     False,      True         ),
+    #   Environment names with "invalid" characters are accepted here; the client is expected to deal with this.
+    ("\x01.-@\x02,xxx", ("\x01.-@\x02", "xxx"), False,      False        ),
+    ],
+)
+def test_clienv(user_input: str, env_names: tuple[str], is_all: bool, is_default: bool) -> None:
+    ce = CliEnv(user_input)
+    assert (ce.is_all, ce.is_default_list, tuple(ce)) \
+        == (is_all,    is_default,         tuple(env_names))
+
+@pytest.mark.parametrize(
+    ("user_input", "expected"),
+    [
+        ("", False),
+        ("all", False),
+        ("All", False),
+        ("ALL", True),
+        ("a,ALL,b", True),
+    ],
+)
+def test_clienv_is_all(user_input: str, expected: bool) -> None:
+    assert CliEnv(user_input).is_all is expected
+
+
 def test_env_select_lazily_looks_at_envs() -> None:
     state = State(get_options(), [])
     env_selector = EnvSelector(state)