diff --git a/beat/core/test/test_format_array.py b/beat/core/test/test_format_array.py
index f3f470283d728bef086a193bb581991e2cd50149..960a04f3564a034706c578a3f0e66f50d0e5f20e 100644
--- a/beat/core/test/test_format_array.py
+++ b/beat/core/test/test_format_array.py
@@ -43,5 +43,7 @@ from . import prefix
 
 def test_array_of_arrays_does_not_validate():
     df = DataFormat(prefix, "user/array_of_array/1")  # not allowed
-    assert df.valid is False
-    assert df.errors[0].find("is not valid under any of the given schemas") != -1
+    nose.tools.assert_false(df.valid)
+    nose.tools.assert_not_equal(
+        df.errors[0].find("is not valid under any of the given schemas"), -1
+    )