tests: time_units: check for overflow in z_tmcvt intermediate

[cfriedt]

This simply adds a unit test for a previous change that went in which did not have an accompanying test.

Prior to #41602, due to the ordering of operations (first mul, then div), an intermediate value would overflow, resulting in a time non-linearity.

Fixes #41111

[mbolivar-nordic]

Not critical or blocking, but this is weird yaml. Does utilities.time_units.z_tmcvt: {} work?

[cfriedt]

I'm a YAML n00b, so my guess is it will. Are there other instances of that in-tree?

[cfriedt]

@mbolivar-nordic - Fixed!

[mbolivar-nordic]

I'm a YAML n00b, so my guess is it will.

I guess you tested it? My working tree is busy with another branch rn, which is why I phrased it as a question

Are there other instances of that in-tree?

I don't know -- did you copy/paste it from somewhere?

My example is definitely valid YAML, it just creates an empty dictionary in the test specification:

In [21]: yaml_str = '''
    ...: common:
    ...:   tags: time_units
    ...:   type: unit
    ...: tests:
    ...:   utilities.time_units.z_tmvct: {}
    ...: '''

In [22]: yaml.safe_load(yaml_str)
Out[22]: 
{'common': {'tags': 'time_units', 'type': 'unit'},
 'tests': {'utilities.time_units.z_tmvct': {}}}

from the comment on line 7 above, it looked to me like someone was looking for a way to have a dict key which mapped to an empty dict, but didn't know how to spell that in YAML.

[cfriedt]

I'm a YAML n00b, so my guess is it will.

I guess you tested it?

Yep

Are there other instances of that in-tree?

I don't know -- did you copy/paste it from somewhere?

There is 1 instance of {} that I have found in-tree with grep and I only learned of it after you mentioned. But no, I did not copy-paste, but knew from my limited yaml experience that empty yaml attributes do not parse properly.

[mbolivar-nordic]

but knew from my limited yaml experience that empty yaml attributes do not parse properlly.

Gotcha. The secret trick is that YAML is actually a superset of JSON, so if you don't know how to do something in YAML but you do in JSON, it works as you'd expect.

As an extreme example:

In [2]: yaml_str = '''{'common': {'tags': 'time_units', 'type': 'unit'},
   ...:  'tests': {'utilities.time_units.z_tmvct': {}}}'''

In [3]: yaml.safe_load(yaml_str)
Out[3]: 
{'common': {'tags': 'time_units', 'type': 'unit'},
 'tests': {'utilities.time_units.z_tmvct': {}}}