ARROW-7980: [Python] Fix creation of tz-aware datetime dtype on first pandas import

python/pyarrow/pandas-shim.pxi

@@ -159,6 +159,7 @@ cdef class _PandasAPIShim(object):
 
     @property
     def datetimetz_type(self):
+        self._check_import()
         return self._datetimetz_type
 
     @property

python/pyarrow/tests/test_schema.py

@@ -70,6 +70,16 @@ def test_type_to_pandas_dtype():
         assert arrow_type.to_pandas_dtype() == numpy_type
 
 
+@pytest.mark.pandas
+def test_type_to_pandas_dtype2():
+    # the types where to_pandas_dtype returns a non-numpy dtype
+    cases = [
+        (pa.timestamp('ns', tz='UTC'), "datetime64[ns, UTC]"),
+    ]
+    for arrow_type, pandas_type in cases:
+        assert str(arrow_type.to_pandas_dtype()) == pandas_type
+
+
 def test_type_list():
     value_type = pa.int32()
     list_type = pa.list_(value_type)