Add null and recursive tests for ValueFormatter

[aerotog]

Helps with #3181. Includes some typo fixes in the same file.

I'm slightly concerned that the serialization result for the primitive 'null' is different for each CaptureType. Please verify the asserted values are expected for each CaptureType:

        [InlineData(CaptureType.Normal, "NULL")]
        [InlineData(CaptureType.Serialize, "null")]
        [InlineData(CaptureType.Stringify, "\"\"")]

[welcome]

Thanks for opening this pull request!
We will try to review this soon! Please note that pull requests with unit tests are earlier accepted 👼

[304NotModified]

Thanks!

I think you found a bug! Have to think about it what's expected output.

[304NotModified]

[InlineData(CaptureType.Normal, "NULL")]

This is expected (in the docs)

    [InlineData(CaptureType.Serialize, "null")]

Serializable should be parseable, so also expected.

    [InlineData(CaptureType.Stringify, "\"\"")]

Doubting about this. Maybe it's nice you could control "" or null, so maybe this is also OK

[welcome]

Hooray your first pull request is merged! Thanks for the contribution! Looking for more? 👼 Please check the up-for-grabs issues - thanks!

[304NotModified]

Merge this one anyway, thanks!!