TST: Add test for categorical with str and tuples

The bug is not present any more.

closes #21416

Author: has2k1

pandas/tests/arrays/categorical/test_constructors.py

@@ -3,6 +3,7 @@
 import numpy as np
 import pytest
 
+from pandas.compat.numpy import _np_version_under1p16
 from pandas.core.dtypes.common import is_float_dtype, is_integer_dtype
 from pandas.core.dtypes.dtypes import CategoricalDtype
 
@@ -601,3 +602,14 @@ def test_constructor_imaginary(self):
         c1 = Categorical(values)
         tm.assert_index_equal(c1.categories, Index(values))
         tm.assert_numpy_array_equal(np.array(c1), np.array(values))
+
+    def test_constructor_string_and_tuples(self):
+        # GH 21416
+        # For NumPy <1.16, np.array(["", ("a",)]) raises
+        # ValueError: setting an array element with a sequence.
+        if _np_version_under1p16:
+            raise pytest.skip("Skipping for NumPy <1.16")
+
+        c = pd.Categorical(["c", ("a", "b"), ("b", "a"), "c"])
+        expected_index = pd.Index([("a", "b"), ("b", "a"), "c"])
+        assert c.categories.equals(expected_index)