tests: add a test cases for _parse_version()

Refactor _parse_version() to make it more testable.
Add unit tests to validate its behavior.

qtpy/__init__.py

@@ -193,15 +193,20 @@ def _parse_int(value):
 
 
 def _parse_version(version):
-    """Parse a version string into a tuple of ints"""
+    """Parse a version into a comparable object"""
     try:
         from packaging.version import parse as _packaging_version_parse
     except ImportError:
-        return tuple(_parse_int(x) for x in version.split("."))
+        return _parse_version_internal(version)
     else:
         return _packaging_version_parse(version)
 
 
+def _parse_version_internal(version):
+    """Parse a version string into a tuple of ints"""
+    return tuple(_parse_int(x) for x in version.split("."))
+
+
 # Unless `FORCE_QT_API` is set, use previously imported Qt Python bindings
 if not os.environ.get("FORCE_QT_API"):
     if "PyQt5" in sys.modules:

qtpy/tests/test_main.py

@@ -5,7 +5,14 @@
 
 import pytest
 
-from qtpy import API_NAMES, QtCore, QtGui, QtWidgets
+from qtpy import (
+    API_NAMES,
+    QtCore,
+    QtGui,
+    QtWidgets,
+    _parse_version,
+    _parse_version_internal,
+)
 from qtpy.tests.utils import pytest_importorskip
 
 with contextlib.suppress(Exception):
@@ -141,3 +148,21 @@ def test_qt_api_environ(api):
     raise AssertionError('QtPy imported despite bad QT_API')
 """
     subprocess.check_call([sys.executable, "-Oc", cmd], env=env)
+
+
+@pytest.mark.parametrize(
+    "first,second",
+    [("1.2.3", "1.2.3.1"), ("1.2.3", "1.10.0")],
+)
+def test_parse_version(first, second):
+    """Verify the behavior of _parse_version()"""
+    assert _parse_version(first) < _parse_version(second)
+
+
+@pytest.mark.parametrize(
+    "value,expect",
+    [("1.2.3", (1, 2, 3)), ("1.x.3", (1, 0, 3))],
+)
+def test_parse_version_internal(value, expect):
+    """Verify the behavior of _parse_version_internal()"""
+    assert _parse_version_internal(value) == expect