Add assertions about multi value query parameters.

[calavera]

Issue #, if available:

Double checking that we're correctly building the request object after seeing #802

Description of changes:

I've added additional assertions to verify that the request object is built correctly.

By submitting this pull request

• [x] I confirm that my contribution is made under the terms of the Apache 2.0 license.
• [x] I confirm that I've made a best effort attempt to update all relevant documentation.