test(common): Derive next_version fixture from TMUX_MAX_VERSION

Author: tony

tests/test_common.py

@@ -32,6 +32,17 @@
 version_regex = re.compile(r"([0-9]\.[0-9])|(master)")
 
 
+def _get_next_tmux_version() -> str:
+    """Derive next tmux version from TMUX_MAX_VERSION.
+
+    Strips trailing letters and increments minor version.
+    E.g., "3.5a" -> "3.6"
+    """
+    base = re.sub(r"[a-z]+$", "", TMUX_MAX_VERSION)
+    major, minor = base.split(".")
+    return f"{major}.{int(minor) + 1}"
+
+
 def test_has_version() -> None:
     """Test has_version()."""
     assert has_version(str(get_version()))
@@ -298,10 +309,10 @@ class VersionParsingFixture(t.NamedTuple):
     ),
     VersionParsingFixture(
         test_id="next_version",
-        mock_stdout=["tmux next-3.6"],
+        mock_stdout=[f"tmux next-{_get_next_tmux_version()}"],
         mock_stderr=None,
         mock_platform=None,
-        expected_version="3.6",
+        expected_version=_get_next_tmux_version(),
         raises=False,
         exc_msg_regex=None,
     ),