ci: adjust to and rename extra-args.yaml to test-extra-args.yaml

I misunderstood extra-args.yaml to be a file that was recognized by
repo2docker's CLI, but in reality it was just a file recognized by the
repo2docker test suite. Following that, I renamed this testing specific
file to test-extra-args.yaml to help others avoid making that mistake
and added comments to clarify that.

This commit also gathers the conda buildpacks separate readme files into
a single readme file.

Author: consideRatio

tests/conda/README.md

@@ -0,0 +1,57 @@
+# Overview of tests for the conda buildpack
+
+## py2
+
+- Test setup of a Python 2 environment by declaring `python=2` in
+  `environment.yml`.
+
+## py35-binder-dir
+
+- Test setup of a Python 3.5 environment by declaring `python=3.5` in
+  `environment.yml`.
+
+  The reasons for testing 3.5 specifically is that it is the oldest version of
+  Python 3 supported by repo2docker's conda buildpack. See
+  `repo2docker/buildpacks/conda` for details.
+
+- Test use of a `.binder` directory, where files outside it shouldn't be
+  considered. See [this documentation](https://repo2docker.readthedocs.io/en/latest/usage.html#where-to-put-configuration-files)
+  for details.
+
+## py310-requirements-file
+
+- Test setup of a Python 3.10 environment by declaring `python=3.10` in
+  `environment.yml`.
+
+  The reasons for testing 3.10 specifically is that it is the newest version of
+  Python 3 supported by repo2docker's conda buildpack. See
+  `repo2docker/buildpacks/conda` for details.
+
+- Test use of a `requirements.txt` file, where an `environment.yml` file should
+  take precedence and the `requirements.txt` should be ignored.
+
+## r-postbuild-file
+
+- Test setup of the default Python environment by omitting `python` from
+  `environment.yml` file.
+
+- Test setup of the default R environment by specifying `r-base` in
+  `environment.yml`.
+
+- Test use of a `postBuild` file. See [this documentation](https://repo2docker.readthedocs.io/en/latest/config_files.html#postbuild-run-code-after-installing-the-environment)
+  for details.
+
+## r3.6-target-repo-dir-flag
+
+- Test setup of a R 3.6 environment by specifying `r-base=3.6` in
+  `environment.yml`.
+
+- Test use of repo2docker with the `--target-repo-dir` flag. See [this documentation](https://repo2docker.readthedocs.io/en/latest/usage.html#cmdoption-jupyter-repo2docker-target-repo-dir)
+  for details.
+
+  `--target-repo-dir` is meant to support custom paths where repositories can be
+  copied to besides `${HOME}`.
+  
+  This test makes use of the `test-extra-args.yaml` file to influence additional
+  arguments passed to `repo2docker` during the test. In this test, specify
+  `--target-repo-dir=/srv/repo`.

tests/conda/py2/README.rst

@@ -1,5 +1,6 @@
 dependencies:
   - python=3.10
   - numpy
+  - pip
   - pip:
-    - simplejson
+      - simplejson