TestCase filter with empty value

[breyed]

It would be good to document in TestCase filter how to pass a --filter to filter a property for no value.

For example, consider a solution where most tests run without any dependencies, and so have no TestCategoryAttribute. However, some tests have dependencies such as other services running, that make them unsuitable for running on a CI build. These have a TestCategoryAttribute that state the dependencies. It would be useful to define a build that runs all the tests with no category. Something like ---filter TestCategory=''. Currently, there doesn't seem to be any documentation on how to do that.

[breyed]

A related topic is that the page doesn't address whitespace in a value or quoting a value. If those were covered, the empty value case be taken care of inherently.