The parsing is based on decode.py.
The basic functionality is implemented, but see the TODO flags.

tested with output of `candump -tA` but not yet with -tz or others or without time stamps

resolved in commit 2480290

bugfix for commit 2480290

A user might want to show some values in the first subplot and all the rest in a second subplot:
$ cat log | cantools plot my.dbc '*device1.current' '*device2.current' - 'current'
Here the data should not be replotted. (But has been before this commit.)

On the other hand a user might want to emphasize the data points in a different color
to see how much time is between two messages:
$ cat log | cantools plot my.dbc '*device1.current:b-' '*device1.current:ro'
In this case the data should be replotted. (But was not before this commit.)

see commit 2480290

by default argparse ignores paragraph ends and lists,
making especially the lists pretty unreadable.
RawDescriptionHelpFormatter does not format description texts.
It does not look good but is a lot better readable.

it seems cleaner to consistently call the functions of the subplot object

This has an effect on the order of the signals in the legend
and will become important for testing.

The order of the legend is now determined by:
1) the order of the matching regex given in the command line options
2) the name of the signal (including the message name as prefix)

I copied them from test_command_line.py but they are misleading
because cantools uses format strings which require python3 (e.g. database/can/formats/arxml.py, line 25).
Therefore the tests cannot pass in python2.

forgotten in commit 3fa9ef9

each test on it's own is passing
but the 2nd test executed fails

bugfix for commit 3fa9ef9
problem became visible in commit b178f9b

In the second test executed the system under test was using the same mock object like in the first test.
But the test was comparing against the new mock object which was empty because it had not been used.
Therefore the test failed.

I have fixed this by mocking matplotlib globally so that all tests use the same mock object which is reset in the test setup.

instead of a list of several regex

This reduces run time from 6:18 min to 5:22 min, i.e. by around 15%,
for around 28.6e6 lines cantools decode output and 9 regex passed as command line arguments.

it actually ignores the information from cantools decode
and only parses the information from candump which is
passed through by cantools decode.
Nevertheless it's important to check that the added strings
don't confuse cantools plot.

idea for `plt.rcParams["date.autoformatter.minute"]` taken from:
https://stackoverflow.com/a/47541788/2828064

The name of the new mock object is arbitrary, it's only purpose is to avoid that it shows up in plt.mock_calls.
https://docs.python.org/3/library/unittest.mock.html#attaching-mocks-as-attributes
> When you attach a mock as an attribute of another mock (or as the return value) it becomes a “child” of that mock. [...]
> The exception to this is if the mock has a name. This allows you to prevent the “parenting” if for some reason you don’t want it to happen.

bug added in commit c7f5fa4.
The tests passed because the changes worked as intended
but matplotlib (which was replaced by a mock) is not able to handle timedelta objects.

Therefore I have added a new test script which does not mock matplotlib.

see commit 02b0258

commit 043fdef
requires two changes to the tests:
- x values are floats instead of timedelta objects (line 1229)
- ignore the axes attribute of subplots which is just cosmetic and not about data (all the rest)

in commit 02b0258
I added test_plot_without_mock.py which passed when run on it's own
but failed when run with `python3 -m unittest discover tests`
because test_plot.py mocked matplotlib and the new test script loaded the mock
instead of the real library.

This is also more elegant because I am not using protected attributes anymore,
compare commit 60abbfa.

belongs to commit 9918e27

The windows have a white background and so does the readme.
Without the border it is not visible that toolbar and plot are in the same image.

not used anymore since commit c7f5fa4

trying to satisfy coveralls
https://coveralls.io/builds/36070444/source?filename=cantools%2Fsubparsers%2Fplot.py#L215

test 1 for commit 2572dc3

test 2 for commit 2572dc3