improve tests for correct preallocation

Author: realead

pandas/tests/libs/test_hashtable.py

@@ -164,14 +164,18 @@ def test_get_state(self, table_type, dtype):
         assert "upper_bound" in state
 
     def test_no_reallocation(self, table_type, dtype):
-        N = 110
-        keys = np.arange(N).astype(dtype)
-        table = table_type(N)
-        n_buckets_start = table.get_state()["n_buckets"]
-        table.map_locations(keys)
-        n_buckets_end = table.get_state()["n_buckets"]
-        # orgininal number of buckets was enough:
-        assert n_buckets_start == n_buckets_end
+        for N in range(1, 110):
+            keys = np.arange(N).astype(dtype)
+            preallocated_table = table_type(N)
+            n_buckets_start = preallocated_table.get_state()["n_buckets"]
+            preallocated_table.map_locations(keys)
+            n_buckets_end = preallocated_table.get_state()["n_buckets"]
+            # orgininal number of buckets was enough:
+            assert n_buckets_start == n_buckets_end
+            # check with clean table (not too much preallocated)
+            clean_table = table_type()
+            clean_table.map_locations(keys)
+            assert n_buckets_start == clean_table.get_state()["n_buckets"]
 
 
 def test_get_labels_groupby_for_Int64(writable):
@@ -209,14 +213,18 @@ def test_tracemalloc_for_empty_StringHashTable():
 
 
 def test_no_reallocation_StringHashTable():
-    N = 110
-    keys = np.arange(N).astype(np.compat.unicode).astype(np.object_)
-    table = ht.StringHashTable(N)
-    n_buckets_start = table.get_state()["n_buckets"]
-    table.map_locations(keys)
-    n_buckets_end = table.get_state()["n_buckets"]
-    # orgininal number of buckets was enough:
-    assert n_buckets_start == n_buckets_end
+    for N in range(1, 110):
+        keys = np.arange(N).astype(np.compat.unicode).astype(np.object_)
+        preallocated_table = ht.StringHashTable(N)
+        n_buckets_start = preallocated_table.get_state()["n_buckets"]
+        preallocated_table.map_locations(keys)
+        n_buckets_end = preallocated_table.get_state()["n_buckets"]
+        # orgininal number of buckets was enough:
+        assert n_buckets_start == n_buckets_end
+        # check with clean table (not too much preallocated)
+        clean_table = ht.StringHashTable()
+        clean_table.map_locations(keys)
+        assert n_buckets_start == clean_table.get_state()["n_buckets"]
 
 
 @pytest.mark.parametrize(