Revised structure for writing example tests

[jpn--]

I am proposing a new structure for writing example tests.

Currently, we write most examples using layered config directories. For example, here we look for settings in three different directories:

activitysim/activitysim/examples/prototype_mtc/test/test_mtc.py

Lines 34 to 39 in 739c2e4

	"-c",
	test_path("configs_mp"),
	"-c",
	example_path("configs_mp"),
	"-c",
	example_path("configs"),

As we have more complicated testing permutations, these can get messy and hard to maintain:

activitysim/activitysim/examples/prototype_mtc_extended/test/test_mtc_extended.py

Lines 86 to 137 in 739c2e4

	shadowprice_configs = (
	[] if shadow_pricing else ["-c", test_path("no-shadow-pricing")]
	)
	if shadow_pricing:
	kwargs["configs_dir"].append(test_path("no-shadow-pricing"))
	if sharrow:
	sh_configs = ["-c", example_path("configs_sharrow")]
	kwargs["configs_dir"].append(example_path("configs_sharrow"))
	else:
	sh_configs = []
	if multiprocess:
	mp_configs = [
	"-c",
	test_path("configs_mp"),
	"-c",
	example_path("configs_mp"),
	]
	kwargs["configs_dir"].append(test_path("configs_mp"))
	kwargs["configs_dir"].append(example_path("configs_mp"))
	elif sharrow:
	mp_configs = [
	"-c",
	test_path("configs"),
	]
	kwargs["configs_dir"].append(test_path("configs"))
	else:
	mp_configs = [
	"-c",
	test_path("configs"),
	]
	kwargs["configs_dir"].append(test_path("configs"))
	run_args = (
	shadowprice_configs
	+ sh_configs
	+ mp_configs
	+ [
	"-c",
	example_path("configs"),
	"-c",
	example_mtc_path("configs"),
	"-d",
	example_mtc_path("data"),
	"-o",
	test_path(f"output_{int(sharrow)}{int(shadow_pricing)}"),
	"--data_model",
	example_path("data_model"),
	]
	)
	kwargs["configs_dir"].append(example_path("configs"))
	kwargs["configs_dir"].append(example_mtc_path("configs"))
	kwargs["data_dir"] = [example_mtc_path("data")]
	kwargs["output_dir"] = test_path("output")

I propose a more direct structure for testing, where there are only a very limited number of "main" config directories, and various permutations for testing are not written out in more config directories, but instead manipulated directly in the Python of the test.

https://github.com/camsys/sandag-abm3-example/blob/6092354290a45aa4b771a8c18910b8bb4cd952de/test/test_sandag_abm3.py#L217-L239

cc @i-am-sijia @dhensle