Given the diversity of information systems today, communication
between services requires that APIs be well designed and understood
by both services producers and consumers. Poorly documented
APIs lead to misunderstandings by developers and testers
teams who end up designing ineffective test cases. As a result, they
may produce software with low quality and avoidable errors. This
study investigates the ability of the SigniFYIng APIs tool to support
the testability of the applications consuming APIs. In this paper, we
proposed a process to support APIs’ testability with the SigniFYIng
APIs tool. We validated the process with a real case study based
on two Brazilian federal government APIs: the leniency agreement
API and the federal servants API. As a result, it was possible to
develop better test cases for the chosen APIs, bringing evidence
that the proposed process can support designing more suitable test
cases for APIs and improving the testability of the software to be
produced.