[3.10] bpo-45578: add tests for dis.distb (GH-29332) (GH-29385)

(cherry picked from commit e346f19681)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

Lib/test/test_dis.py

@@ -1244,5 +1244,46 @@ class TestBytecodeTestCase(BytecodeTestCase):
         with self.assertRaises(AssertionError):
             self.assertNotInBytecode(code, "LOAD_CONST", 1)
 
+
+class TestDisTraceback(unittest.TestCase):
+    def setUp(self) -> None:
+        try:  # We need to clean up existing tracebacks
+            del sys.last_traceback
+        except AttributeError:
+            pass
+        return super().setUp()
+
+    def get_disassembly(self, tb):
+        output = io.StringIO()
+        with contextlib.redirect_stdout(output):
+            dis.distb(tb)
+        return output.getvalue()
+
+    def test_distb_empty(self):
+        with self.assertRaises(RuntimeError):
+            dis.distb()
+
+    def test_distb_last_traceback(self):
+        # We need to have an existing last traceback in `sys`:
+        tb = get_tb()
+        sys.last_traceback = tb
+
+        self.assertEqual(self.get_disassembly(None), dis_traceback)
+
+    def test_distb_explicit_arg(self):
+        tb = get_tb()
+
+        self.assertEqual(self.get_disassembly(tb), dis_traceback)
+
+
+class TestDisTracebackWithFile(TestDisTraceback):
+    # Run the `distb` tests again, using the file arg instead of print
+    def get_disassembly(self, tb):
+        output = io.StringIO()
+        with contextlib.redirect_stdout(output):
+            dis.distb(tb, file=output)
+        return output.getvalue()
+
+
 if __name__ == "__main__":
     unittest.main()