Add unit test of cypclass' isinstanceof

tests/run/cypclass_isinstanceof.pyx

+# mode: run
+# tag: cpp, cpp11
+# cython: experimental_cpp_class_def=True, language_level=2
+
+cdef cypclass Base:
+    pass
+
+cdef cypclass Derived(Base):
+    pass
+
+def test_insinstanceof():
+    """
+    >>> test_insinstanceof()
+    (1, 1, 1, 0, 1, 1)
+    """
+    cdef Base base = Base()
+    cdef Base derived_as_base = Derived()
+    cdef Derived derived = Derived()
+
+    cdef int r1 = isinstanceof[Base](base)
+    cdef int r2 = isinstanceof[Base](derived_as_base)
+    cdef int r3 = isinstanceof[Base](derived)
+
+    cdef int r4 = isinstanceof[Derived](base)
+    cdef int r5 = isinstanceof[Derived](derived_as_base)
+    cdef int r6 = isinstanceof[Derived](derived)
+
+    print(r1, r2, r3, r4, r5, r6)
\ No newline at end of file