rust-python-testing: separated base test classes

This will allow, e.g., to change `test-rust-discovery.py` simply
by adding the appropriate base class.

mercurial/testing/revlog.py

@@ -45,8 +45,17 b' class RevlogBasedTestBase(unittest.TestC'
             data = data_non_inlined
         return cparsers.parse_index2(data, False)[0]
 
+
[e-mail](
+    MixedIndex is None,
+    'The Rust index is not available. It is needed for this test.',
+)
+class RustRevlogBasedTestBase(unittest.TestCase):
     def parserustindex(self, data=None):
         if data is None:
             data = data_non_inlined
-        cindex = self.parseindex(data=data)
+        # not inheriting RevlogBasedTestCase to avoid having a
+        # `parseindex` method that would be shadowed by future subclasses
+        # this duplication will soon be removed
+        cindex = cparsers.parse_index2(data, False)[0]
         return MixedIndex(cindex, data, REVLOGV1)

tests/test-rust-ancestor.py

@@ -36,7 +36,7 b' except ImportError:'
     'The Rust or C version of the "parsers" module, which the "ancestor" module'
     ' relies on, is not available.',
 )
-class rustancestorstest(revlogtesting.RevlogBasedTestBase):
+class rustancestorstest(revlogtesting.RustRevlogBasedTestBase):
     """Test the correctness of binding to Rust code.
 
     This test is merely for the binding to Rust itself: extraction of