The transport class under test.
ReadonlyclientThe transport instance, of the class handed over.
ReadonlyrequestThe spy on the transport's request: stub it, then assert on its
calls. Spelled as the method's own signature rather than
HttpClient['request'], so the docs do not inherit the method's
comment into a module that cannot resolve its links.
A transport and the spy on its
request, as createMockHttpClient builds them.