Add coverage for both expression and dataframe filter

[wence-]

Description

Note that expression filter with literals does not work because broadcasting is not implemented. It is also the case that the result could be computed without broadcasting in the case of scalars with some data introspection, but we do not do that here.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[wence-]

/merge