Bug report

Bug summary

The tests for LogFormatter do not explicitly test the return value of __call__ which allowed this bug #8594 to slip through.

We extensively test pprint_val and that __call__ correctly skips formatting ticks when required

Code for reproduction

(prior to merging and backporting #8594 )

In [31]: fig, ax = plt.subplots()

In [32]: ax.xaxis.set_major_formatter(lf)

In [33]: lf(5)
Out[33]: ''

In [34]: lf(50)
Out[34]: ''

In [35]: lf(100)

In [36]: print(str(lf(100)))
None

In [37]: print(str(lf(1)))
None

In [38]: print(str(lf(10)))
None

In [39]: print(str(lf(10000)))
None

Actual outcome

Expected outcome

Not None!

Matplotlib version

• Operating System: any
• Matplotlib Version: 2.0-2.0.1
• Python Version: any
• Jupyter Version (if applicable):
• Other Libraries: