Add tests for histogram plotting

[dakshvar22]

Description of Problem:
Currently there are no tests for histogram plotting inside rasa/utils/plotting.py(def plot_histogram). These should be added, specifically related to the logic of creation of bins.

Overview of the Solution:
Tests for the above function

[ericoBandeira]

Hi, has this issue been solved?

[JEM-Mosig]

@ericoBandeira I was just about to pick it up. Do you want to do it?

[ericoBandeira]

@JEM-Mosig I would like to solve this issue! thank you so much

[JEM-Mosig]

@ericoBandeira Ok, great! Go ahead :) You can assign me to review your PR when you're ready.

[santosm46]

@JEM-Mosig Hello! I'm working with @ericoBandeira and I have a question, where should the test be created? as def plot_histogram returns None, I think it has to be at rasa/utils/test.py where there is a function calling plot_curve from rasa.utils.plotting, it returns None such as def plot_histogram.
Also, could you please give more details that can help us to solve this?

[JEM-Mosig]

@santosm46 @ericoBandeira The test should be in a new tests/utils/test_plotting.py file. I'd recommend splitting the plot_histogram function into two parts: One (set of) function(s) that computes the bin specification and one function that does the matplotlib stuff. The former part is essentially everything that happens before fig, axes = plt.subplots(...) and is the part that need tests.

[JEM-Mosig]

@santosm46 @ericoBandeira How is this coming along?

[santosm46]

Hi @JEM-Mosig
We're no longer working on this issue, thanks for the attention. Anyone can feel free to work on it.

[JEM-Mosig]

Oh, ok. I'll pick it up then.

[JEM-Mosig]

Looking into it, I just notice that the plot is missing some data (cutoffs are wrong). E.g. for:

[[1., 3., 8.], [2., 3., 3.]]

the left histogram only shows two bars, even though it should be three. Will fix this with this issue, too.