Update tests.md for new test directories

Author: mathbunnyru

docs/contributing/tests.md

@@ -4,17 +4,17 @@ We greatly appreciate Pull Requests that extend the automated tests that vet the
 
 ## How the Tests Work
 
-A [GitHub Action workflow](https://github.com/jupyter/docker-stacks/blob/main/.github/workflows/docker.yml)
+A [GitHub Action workflow](https://github.com/jupyter/docker-stacks/blob/main/.github/workflows/docker-build-test-upload.yml)
 runs tests against pull requests submitted to the `jupyter/docker-stacks` repository.
 
 We use the `pytest` module to run tests on the image.
 `conftest.py` and `pytest.ini` in the `tests` folder define the environment in which tests are run.
 More info on `pytest` can be found [here](https://docs.pytest.org/en/latest/contents.html).
 
-The actual image-specific test files are located in folders like `tests/<somestack>/` (e.g., `tests/docker-stacks-foundation/`, `tests/minimal-notebook/`, etc.).
+The actual image-specific test files are located in folders like `tests/by_image/<somestack>/` (e.g., `tests/by_image/docker-stacks-foundation/`, etc.).
 
 ```{note}
-If your test is located in `tests/<somestack>/`, it will be run against the `jupyter/<somestack>` image and against all the [images inherited from this image](https://jupyter-docker-stacks.readthedocs.io/en/latest/using/selecting.html#image-relationships.
+If your test is located in `tests/by_image/<somestack>/`, it will be run against the `jupyter/<somestack>` image and against all the [images inherited from this image](https://jupyter-docker-stacks.readthedocs.io/en/latest/using/selecting.html#image-relationships).
 ```
 
 Many tests make use of global [pytest fixtures](https://docs.pytest.org/en/latest/reference/fixtures.html)
@@ -23,15 +23,15 @@ defined in the [conftest.py](https://github.com/jupyter/docker-stacks/blob/main/
 ## Unit tests
 
 You can add a unit test if you want to run a Python script in one of our images.
-You should create a `tests/<somestack>/units/` directory, if it doesn't already exist, and put your file there.
+You should create a `tests/by_image/<somestack>/units/` directory, if it doesn't already exist, and put your file there.
 Files in this folder will be executed in the container when tests are run.
-You can see an [TensorFlow package example here](https://github.com/jupyter/docker-stacks/blob/HEAD/tests/tensorflow-notebook/units/unit_tensorflow.py).
+You can see an [TensorFlow package example here](https://github.com/jupyter/docker-stacks/blob/HEAD/tests/by_image/tensorflow-notebook/units/unit_tensorflow.py).
 
 ## Contributing New Tests
 
 Please follow the process below to add new tests:
 
-1. Add your test code to one of the modules in the `tests/<somestack>/` directory or create a new module.
+1. Add your test code to one of the modules in the `tests/by_image/<somestack>/` directory or create a new module.
 2. Build one or more images you intend to test and run the tests locally.
    If you use `make`, call: