In addition to testing to_api_repr(), I think we also need to test against the class property itself, and also from_api_repr().

I think the original author of this test file (specifically test_external_config.py) designed it to perform the tests you are discussing, even if it is not immediately apparent and would argue the current state is satisfactory:

• the new attribute (time_zone) is tested in test_to_api_repr_base()
• the new attribute is tested in test_from_api_repr_base()
• during the above tests, we also explicitly test the getter and setter for the new attribute

If we decide that this pattern/philosophy is not satisfactory, then it seems that we will need to completely rewrite this file from top to bottom.

See below for a walkthrough:

TestExternalConfig.test_to_api_repr_base()

• We create an ExternalConfig object (ec) from the ExternalConfig class
• We then set each class attribute individually (ec.autodetect=True, ec.time_zone=self.TIME_ZONE, etc)
  • by default, this tests the setter for each attribute covered by BASE_RESOURCE including time_zone
• We use ec.to_api_repr() to create got_resource. This tests the ability to use to_api_repr()
• We compare got_resource to exp_resource (which includes all the attributes we just set) ensuring that to_api_repr() performed as expected

TestExternalConfig.test_from_api_repr_base()

• Also relies on BASE_RESOURCE to facilitate testing
• we use from_api_repr() to create an ExternalConfig object (ec) based on BASE_RESOURCE #L43
• we use _verify_base() to ensure that the ec object matches the expected values from BASE_RESOURCE #L44 & #L129
  • by default, this tests the getter for each attribute covered by BASE_RESOURCE including time_zone
  • it is intended to check every single item in BASE_RESOURCE (as long as it and BASE_RESOURCE are in sync)
• we then update the api_repr with more elements (schema and fields, etc) #L51
• we use _verify_base() again to ensure that the expected values from BASE_RESOURCE are present along with the additional elements #L67

If we look at the remainder of the file, we see this pattern repeated several times. Looking at:

• test_from_api_repr_csv
• test_to_api_repr_csv
• test_from_api_repr_bigtable
• test_to_api_repr_bigtable

we see this philosophy and pattern repeated almost exactly.

Regarding adding a to_api_repr and from_api_repr pair, there may be some merit to creating a single test that includes all the attributes as part of a BASE_RESOURCE much as we see in test_external_config.py

Similar to https://github.com/googleapis/python-bigquery/pull/2229/files#r2191183829, I think in general we need to test against to/from_api_repr and the property itself. The same goes for LoadJobConfig and LoadJob. Could you add these changes? Otherwise the PR looks good in general.

The pattern/philosophy for test_load_config.py is different than the approach used in test_external_config.py

Here, the author chose to test each attribute in more of a stand alone fashion using a trifecta of tests:

• x_missing()
• x_hit()
• x_setter()

But:
the author did not test to_api_repr() or from_api_repr() directly (I can add such a pair of tests).

Examples:

• def test_write_disposition_missing()
• def test_write_disposition_hit()
• def test_write_disposition_setter()
• def test_time_zone_missing()
• def test_time_zone_hit()
• def test_time_zone_setter()

missing

Confirms that when the target class is created, the attribute is not populated

self.assertIsNone(config.write_disposition)`

hit

Sets (behind the scenes using ._properties) the value of the attribute
Confirms that the getter functions correctly and that the expected/result values match

config._properties["load"]["writeDisposition"] = write_disposition
self.assertEqual(config.write_disposition, write_disposition)

setter

Sets the value of the attribute directly using the setter function
Confirms that the setter functions correctly by examining the _properties object directly

config.write_disposition = write_disposition
self.assertEqual(config._properties["load"]["writeDisposition"], write_disposition)

I added a test_to_api_repr() and a test_from_api_repr() test because the original file did not include them.