Fixtures making IntNA tests difficult to run interactively
Trying to run tests.arrays.test_integer TestArithmeticOps.test_error in the REPL, need to produce the `data` arg that gets passed to `test_error`.  `data` is defined in a fixture:

```
@pytest.fixture(params=[Int8Dtype, Int16Dtype, Int32Dtype, Int64Dtype,
                        UInt8Dtype, UInt16Dtype, UInt32Dtype, UInt64Dtype])
def dtype(request):
    return request.param()


@pytest.fixture
def data(dtype):
    return integer_array(make_data(), dtype=dtype)
```

Trying to do this manually:

```
>>> from pandas.tests.arrays.test_integer import *
>>> dtype = Int64Dtype
>>>
>>> d = make_data()
>>> dat = integer_array(d, dtype=dtype)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pandas/core/arrays/integer.py", line 104, in integer_array
    values, mask = coerce_to_array(values, dtype=dtype, copy=copy)
  File "pandas/core/arrays/integer.py", line 159, in coerce_to_array
    raise ValueError("invalid dtype specified {}".format(dtype))
ValueError: invalid dtype specified <class 'pandas.core.arrays.integer.Int64Dtype'>
```

What am I missing here?  Figuring out exactly what is tested _should_ be really easy.