Add all_type_info_check_for_divergence() and some tests.

tests/test_python_multiple_inheritance.py

@@ -1,6 +1,8 @@
 # Adapted from:
 # https://github.com/google/clif/blob/5718e4d0807fd3b6a8187dde140069120b81ecef/clif/testing/python/python_multiple_inheritance_test.py
 
+import pytest
+
 from pybind11_tests import python_multiple_inheritance as m
 
 
@@ -12,6 +14,22 @@ class PPCC(PC, m.CppDrvd):
     pass
 
 
+class PPPCCC(PPCC, m.CppDrvd2):
+    pass
+
+
+class PC1(m.CppDrvd):
+    pass
+
+
+class PC2(m.CppDrvd2):
+    pass
+
+
+class PCD(PC1, PC2):
+    pass
+
+
 def test_PC():
     d = PC(11)
     assert d.get_base_value() == 11
@@ -33,3 +51,21 @@ def test_PPCC():
     d.reset_base_value_from_drvd(30)
     assert d.get_base_value() == 30
     assert d.get_base_value_from_drvd() == 30
+
+
+def NOtest_PPPCCC():
+    # terminate called after throwing an instance of 'pybind11::error_already_set'
+    # what():  TypeError: bases include diverging derived types:
+    #     base=pybind11_tests.python_multiple_inheritance.CppBase,
+    #     derived1=pybind11_tests.python_multiple_inheritance.CppDrvd,
+    #     derived2=pybind11_tests.python_multiple_inheritance.CppDrvd2
+    PPPCCC(11)
+
+
+def test_PCD():
+    # This escapes all_type_info_check_for_divergence() because CppBase does not appear in bases.
+    with pytest.raises(
+        TypeError,
+        match=r"CppDrvd2\.__init__\(\) must be called when overriding __init__$",
+    ):
+        PCD(11)