use "with environment_variable(...)"

[ThomasWaldmann]

there are some places in the tests that could use this.

it is a context manager that remembers state of environment vars, sets the env vars as given in kwargs, executes the block, and finally restores the previous state of the environment vars.

[enkore]

pytest monkeypatch can do this as well - but not for unittest.TestCase test methods... so at some point (when client tests are py.test-style) that can be removed. In the meantime it's best to use env_var for unittest-based stuff and monkeypatch where py.test is already used.

[ThomasWaldmann]

todo b7:

• replace environment_variable with monkeypatch.setenv (it is all pytest now).
• remove environment_variable if no users left