Thank you for your question.
There's information on the department's website. You're quite correct in that a citizenship applicant can go to one of the third party test bodies that meet our criteria for tests to be equivalent with the Canadian language benchmark, CLB, level 4, which is a basic official language capacity. There is a range of other forms of evidence that the department accepts, such as academic evidence, evidence that the person has been through language Instruction for newcomers, settlement training that the government funds, which is free and the person has obtained a certificate indicating that the CLB level 4 has been obtained.
Applicants do have a number of types of evidence that they can either pay for or get for free at their disposal.