added errors message; added tests

Author: anmyachev

pandas/core/tools/datetimes.py

@@ -62,8 +62,9 @@ def should_cache(arg, check_count: int, unique_share: float):
     -------
     do_caching: bool
     """
-    assert 0 < check_count <= len(arg)
-    assert 0 < unique_share < 1
+    assert 0 < check_count <= len(arg), ('check_count must be in next bounds: '
+                                         '(0; len(arg)]')
+    assert 0 < unique_share < 1, 'unique_share must be in next bounds: (0; 1)'
 
     do_caching = True
 

pandas/tests/indexes/datetimes/test_tools.py

@@ -2032,3 +2032,23 @@ def test_arg_tz_ns_unit(self, offset, utc, exp):
         result = to_datetime([arg], unit='ns', utc=utc)
         expected = to_datetime([exp])
         tm.assert_index_equal(result, expected)
+
+
+@pytest.mark.parametrize('listlike,do_caching', [
+    ([1, 2, 3, 4, 5, 6, 7, 8, 9, 0], False),
+    ([1, 1, 1, 1, 4, 5, 6, 7, 8, 9], True)
+])
+def test_should_cache(listlike, do_caching):
+    assert tools.should_cache(listlike, check_count=len(listlike),
+                              unique_share=0.7) == do_caching
+
+
+@pytest.mark.parametrize('check_count,unique_share, err_message', [
+    (11, 0.5, r'check_count must be in next bounds: \(0; len\(arg\)]'),
+    (10, 2, r'unique_share must be in next bounds: \(0; 1\)')
+])
+def test_should_cache_errors(check_count, unique_share, err_message):
+    arg = [5] * 10
+
+    with pytest.raises(AssertionError, match=err_message):
+        tools.should_cache(arg, check_count, unique_share)