[doc] add testing guidelines, general improvements

docs/development/testing.rst

@@ -0,0 +1,33 @@
+Testing guidelines
+==================
+
+Writing unit tests
+------------------
+
+Some general hints:
+
+- Tests should run with just Python Standard Library modules installed
+  (i.e. if there are additional requirements, the test should be skipped
+  if those are missing)
+- Tests should run even if there is no network connectivity (please mock
+  urllib calls, for example)
+- Tests should be stable and not require modifications every time the
+  tested code's implementation changes slightly (been there / done that)
+
+Right now, ``bumblebee-status`` uses the ``pytest`` framework, and its
+unit tests are located inside the ``tests/`` subdirectory.
+
+First implication: To run the new tests, you need to have ``pytest``
+installed, it is not part of the Python Standard Library. Most
+distributions call the package ``python-pytest`` or ``python3-pytest``
+or something similar (or you just use ``pip install --use pytest``)
+
+Aside from that, you just write your tests using ``pytest`` as usual,
+with one big caveat:
+
+**If** you create a new directory inside ``tests/``, you need to
+also create a file called ``__init__.py`` inside that, otherwise,
+modules won't load correctly.
+
+For examples, just browse the existing code. A good, minimal sample
+for unit testing ``bumblebee-status`` is ``tests/core/test_event.py``.