tests/basics: Add test for weakref having exception in callback.

Needs a native exp file because native code doesn't print line numbers in
the traceback.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

tests/basics/weakref_callback_exception.py

@@ -0,0 +1,42 @@
+# Test weakref ref/finalize raising an exception within the callback.
+#
+# This test has different output to CPython due to the way that MicroPython
+# prints the exception.
+
+try:
+    import weakref
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+import gc
+
+
+class A:
+    def __str__(self):
+        return "<A object>"
+
+
+def callback(*args):
+    raise ValueError("weakref callback", args)
+
+
+def test():
+    print("test ref with exception in the callback")
+    a = A()
+    r = weakref.ref(a, callback)
+    a = None
+    clean_the_stack = [0, 0, 0, 0]
+    gc.collect()
+    print("collect done")
+
+    print("test finalize with exception in the callback")
+    a = A()
+    weakref.finalize(a, callback)
+    a = None
+    clean_the_stack = [0, 0, 0, 0]
+    gc.collect()
+    print("collect done")
+
+
+test()

tests/basics/weakref_callback_exception.py.exp

@@ -0,0 +1,12 @@
+test ref with exception in the callback
+Unhandled exception in weakref callback:
+Traceback (most recent call last):
+  File "\.\+weakref_callback_exception.py", line 21, in callback
+ValueError: ('weakref callback', (<ref>,))
+collect done
+test finalize with exception in the callback
+Unhandled exception in weakref callback:
+Traceback (most recent call last):
+  File "\.\+weakref_callback_exception.py", line 21, in callback
+ValueError: ('weakref callback', ())
+collect done

tests/basics/weakref_callback_exception.py.native.exp

@@ -0,0 +1,8 @@
+test ref with exception in the callback
+Unhandled exception in weakref callback:
+ValueError: ('weakref callback', (<ref>,))
+collect done
+test finalize with exception in the callback
+Unhandled exception in weakref callback:
+ValueError: ('weakref callback', ())
+collect done

tests/run-tests.py

@@ -158,6 +158,7 @@
     "webassembly": (
         "basics/string_format_modulo.py",  # can't print nulls to stdout
         "basics/string_strip.py",  # can't print nulls to stdout
+        "basics/weakref_callback_exception.py",  # has different exception printing output
         "basics/weakref_ref_collect.py",  # requires custom test due to GC behaviour
         "basics/weakref_finalize_collect.py",  # requires custom test due to GC behaviour
         "extmod/asyncio_basic2.py",
@@ -435,6 +436,7 @@ def detect_target_wiring_script(pyb, args):
         "micropython/meminfo.py",
         "basics/bytes_compare3.py",
         "basics/builtin_help.py",
+        "basics/weakref_callback_exception.py",
         "misc/sys_settrace_cov.py",
         "net_inet/tls_text_errors.py",
         "thread/thread_exc2.py",