tests: Add regression test for r.his

[mshukuno]

Description

Added regression test for r.his.

Motivation and context

There was no testing for r.his.

How has this been tested?

Locally tested with python <path>/raster/r.his/testsuite/test_r_his.py

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to not work as before)
• New test (non-breaking change which adds test)

Checklist

• PR title provides summary of the changes and starts with one of the
  pre-defined prefixes
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[petrasovaa]

Failing with

======================================================================
FAIL: test_bgcolor_none (__main__.TestRHis)
Test r.his with bgcolor 'none'
----------------------------------------------------------------------
Traceback (most recent call last):
  File "raster/r.his/testsuite/test_r_his.py", line 50, in test_bgcolor_none
    self.assertRasterFitsUnivar(
  File "etc/python/grass/gunittest/case.py", line 290, in assertRasterFitsUnivar
    self.assertModuleKeyValue(
  File "etc/python/grass/gunittest/case.py", line 272, in assertModuleKeyValue
    self.fail(self._formatMessage(msg, stdMsg))
AssertionError: r.univar map=shadedmap_r percentile=90.0 nprocs=1 separator== format=plain -g difference:
mismatch values (key, reference, actual): [('max', 255, 198), ('mean', 156.41168, 158.437142857143), ('min', 3, 106), ('null_cells', 5696, 1009900), ('stddev', 34.434612, 30.7161715035702)]
command: r.univar map=shadedmap_r percentile=90.0 nprocs=1 separator== format=plain -g {'map': 'shadedmap_r', 'separator': '=', 'flags': 'g'}

======================================================================
FAIL: test_with_bgcolor_rgb (__main__.TestRHis)
Test r.his with bgcolor '0:0:0'
----------------------------------------------------------------------
Traceback (most recent call last):
  File "raster/r.his/testsuite/test_r_his.py", line 76, in test_with_bgcolor_rgb
    self.assertRasterFitsUnivar(
  File "etc/python/grass/gunittest/case.py", line 290, in assertRasterFitsUnivar
    self.assertModuleKeyValue(
  File "etc/python/grass/gunittest/case.py", line 272, in assertModuleKeyValue
    self.fail(self._formatMessage(msg, stdMsg))
AssertionError: r.univar map=shadedmap_r percentile=90.0 nprocs=1 separator== format=plain -g difference:
mismatch values (key, reference, actual): [('max', 255, 198), ('mean', 155.97172, 0.109742727092816), ('stddev', 35.36988, 4.24603246352255)]
command: r.univar map=shadedmap_r percentile=90.0 nprocs=1 separator== format=plain -g {'map': 'shadedmap_r', 'separator': '=', 'flags': 'g'}

[echoix]

I didn't analyze to look for what isn't there, but what is there makes sense ;)

Thanks for a new test on a module that didn't have some yet!