tests/basics: Add test for calling a subclass of a native class.

Adding this test gets py/objtype.c to 100% coverage.

tests/basics/subclass_native_call.py

@@ -0,0 +1,30 @@
+# test calling a subclass of a native class that supports calling
+
+# For this test we need a native class that can be subclassed (has make_new)
+# and is callable (has call).  The only one available is machine.Signal, which
+# in turns needs PinBase.
+try:
+    import umachine as machine
+except ImportError:
+    import machine
+try:
+    machine.PinBase
+    machine.Signal
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
+class Pin(machine.PinBase):
+    #def __init__(self):
+    #    self.v = 0
+
+    def value(self, v=None):
+        return 42
+
+class MySignal(machine.Signal):
+    pass
+
+s = MySignal(Pin())
+
+# apply call to the subclass, which should call the native base
+print(s())

tests/basics/subclass_native_call.py.exp

@@ -0,0 +1 @@
+42