For the IELTS (International English Language Testing System) test, it's important to understand the guidelines and rules set by the exam administrators. the standard policy was to use either American English or British English consistently throughout all parts of the test. This means that if you choose to use American English spelling in the writing test, you should also use American English spelling in the speaking test.
Consistency is crucial in language testing, as it ensures fair evaluation of candidates' language abilities and prevents any potential advantages or disadvantages based on dialect or spelling preferences.
However, the policies or guidelines for language testing may evolve over time, so I highly recommend checking the official IELTS website or contacting the test center directly to confirm the current rules and requirements regarding language usage in the test. This way, you can be certain about what is allowed and expected during your examination.