Which targets need their requirements in “Build-Depends*” declared?

[Ben Finney <ben+debian@benfinney.id.au>]

Howdy all,

Which of the standard ‘debian/rules’ targets need their requirements
declared in “Build-Depends” (and “Build-Depends-Indep”)?

Policy §7.7 says:

    Source packages that require certain binary packages to be installed
    or absent at the time of building the package can declare
    relationships to those binary packages.

    This is done using the `Build-Depends', `Build-Depends-Indep',
    `Build-Conflicts' and `Build-Conflicts-Indep' control fields.

What standard targets does this “at the time of building the package”
entail? The “test” target? The “get-orig-source” target? What official
set of standard targets obligate their requirements to be declared in
this field?

Note that I'm not looking for opinions about what would be a good idea;
I'm looking for how this policy section is interpreted for normative
behaviour.

-- 
 \         “Pinky, are you pondering what I'm pondering?” “I think so, |
  `\     Brain, but there's still a bug stuck in here from last time.” |
_o__)                                           —_Pinky and The Brain_ |
Ben Finney