test the hashes are unique

Author: ngoldbaum

stringdtype/tests/test_stringdtype.py

@@ -49,17 +49,24 @@ def dtype(na_object, coerce):
 
 
 def test_dtype_creation():
+    hashes = set()
     dt = StringDType()
     assert not hasattr(dt, "na_object") and dt.coerce == 1
+    hashes.add(hash(dt))
 
     dt = StringDType(na_object=None)
     assert dt.na_object is None and dt.coerce == 1
+    hashes.add(hash(dt))
 
     dt = StringDType(coerce=False)
     assert not hasattr(dt, "na_object") and dt.coerce == 0
+    hashes.add(hash(dt))
 
     dt = StringDType(na_object=None, coerce=False)
     assert dt.na_object is None and dt.coerce == 0
+    hashes.add(hash(dt))
+
+    assert len(hashes) == 4
 
 
 def test_scalar_creation():