MAINT: dir(numpy) returned duplicate "testing" (gh-15425)

Modified __dir__() to remove duplicate "Tester/Testing" attribute. Also added a test to verify this.

Closes gh-15383

2 files changed, 7 insertions, 1 deletions

diff --git a/numpy/__init__.py b/numpy/__init__.py
index 00c4a3d78..c5c58b020 100644
--- a/numpy/__init__.py
+++ b/numpy/__init__.py
@@ -215,7 +215,7 @@ else:
                                      "{!r}".format(__name__, attr))
 
         def __dir__():
-            return list(globals().keys()) + ['Tester', 'testing']
+            return list(globals().keys() | {'Tester', 'testing'})
 
     else:
         # We don't actually use this ourselves anymore, but I'm not 100% sure that
diff --git a/numpy/tests/test_public_api.py b/numpy/tests/test_public_api.py
index b4aa7ec3d..27ff87f49 100644
--- a/numpy/tests/test_public_api.py
+++ b/numpy/tests/test_public_api.py
@@ -94,6 +94,12 @@ def test_import_lazy_import(name):
     assert name in dir(np)
 
 
+def test_dir_testing():
+    """Assert that output of dir has only one "testing/tester"
+    attribute without duplicate"""
+    assert len(dir(np)) == len(set(dir(np)))
+    
+
 def test_numpy_linalg():
     bad_results = check_dir(np.linalg)
     assert bad_results == {}