Ensure tests representing containing types of suites are synthesized if necessary

[stmontgomery]

[One line description of your change]

Motivation:

[Explain here the context, and why you're making that change. What is the problem you're trying to solve.]

Modifications:

[Describe the modifications you've done.]

Checklist:

• [ ] Code and documentation should follow the style of the Style Guide.
• [ ] If public symbols are renamed or modified, DocC references should be updated.

Resolves rdar://127770218