Documentation about Mercurial support

docs/source/contributing/tasks.md

@@ -23,11 +23,15 @@ If you want to run a specific test, you can do so with:
 py.test -s tests/<path-to-test>
 ```
 
+To skip the tests related to Mercurial repositories (to avoid to install
+Mercurial or hg-evolve), one can use the environment variables
+``REPO2DOCKER_SKIP_HG_TESTS`` or ``REPO2DOCKER_SKIP_HG_EVOLVE_TESTS``.
+
 ### Troubleshooting Tests
 
 Some of the tests have non-python requirements for your development machine. They are:
 
-- `git-lfs` must be installed ([instructions](https://github.com/git-lfs/git-lfs)). It need not be activated -- there is no need to run the `git lfs install` command. It just needs to be available to the test suite. 
+- `git-lfs` must be installed ([instructions](https://github.com/git-lfs/git-lfs)). It need not be activated -- there is no need to run the `git lfs install` command. It just needs to be available to the test suite.
    - If your test failure messages include "`git-lfs filter-process: git-lfs: command not found`", this step should address the problem.
 
 - Minimum Docker Image size of 128GB is required. If you are not running docker on a linux OS, you may need to expand the runtime image size for your installation. See Docker's instructions for [macOS](https://docs.docker.com/docker-for-mac/space/) or [Windows 10](https://docs.docker.com/docker-for-windows/#resources) for more information.
@@ -218,7 +222,7 @@ files accordingly.
 ## Compare generated Dockerfiles between repo2docker versions
 
 For larger refactorings it can be useful to check that the generated Dockerfiles match
-between an older version of r2d and the current version. The following shell script 
+between an older version of r2d and the current version. The following shell script
 automates this test.
 
 ```bash
@@ -231,7 +235,7 @@ basename="dockerfilediff"
 diff_r2d_dockerfiles_with_version () {
     docker run --rm -t -v "$(pwd)":"$(pwd)" --user 1000 jupyterhub/repo2docker:"$1" jupyter-repo2docker --no-build --debug "$(pwd)" &> "$basename"."$1"
     jupyter-repo2docker --no-build --debug "$(pwd)" &> "$basename"."$current_version"
-    
+
     # remove first line logging the path
     sed -i '/^\[Repo2Docker\]/d' "$basename"."$1"
     sed -i '/^\[Repo2Docker\]/d' "$basename"."$current_version"

docs/source/install.rst

@@ -22,6 +22,17 @@ The `BinderHub <https://binderhub.readthedocs.io/>`_ helm chart uses version
 `helm chart <https://github.com/jupyterhub/binderhub/blob/master/helm-chart/binderhub/values.yaml#L167>`_
 for more details.
 
+Optional: Mercurial
+-------------------
+
+For `Mercurial <https://www.mercurial-scm.org>`_ repositories, `Mercurial needs
+to be installed <https://www.mercurial-scm.org/download>`_. For support of
+`Mercurial topics
+<https://www.mercurial-scm.org/doc/evolution/tutorials/topic-tutorial.html>`_,
+also install `hg-evolve <https://www.mercurial-scm.org/doc/evolution/>`_ which
+provides the topic extension (however, no need to explicitly enable it in a
+Mercurial configuration file).
+
 Installing with ``pip``
 -----------------------
 

tests/unit/contentproviders/test_mercurial.py

@@ -29,6 +29,11 @@
 
 @skip_if_no_hg_tests
 def test_if_mercurial_is_available():
+    """
+    To skip the tests related to Mercurial repositories (to avoid to install
+    Mercurial), one can use the environment variable
+    REPO2DOCKER_SKIP_HG_TESTS.
+    """
     subprocess.check_output(["hg", "version"])
 
 
@@ -134,6 +139,10 @@ def test_bad_ref(hg_repo_with_content):
 def test_ref_topic(hg_repo_with_content):
     """
     Test trying to update to a topic
+
+    To skip this test (to avoid to install hg-evolve), one can use the
+    environment variable REPO2DOCKER_SKIP_HG_EVOLVE_TESTS.
+
     """
     upstream, node_id = hg_repo_with_content
     node_id = subprocess.Popen(