Assessment is often used to promote learning, but the mechanisms of how assessment relates to epistemology -- knowledge and knowing -- have been scarcely studied and theorised. In this study, we examine students' epistemic resources in relation assessment in the context of university mathematics education. We draw on the theoretical framework of epistemic injustice in order to understand how assessment produces knowledge and knowers. Using reflexive thematic analysis, we analyse 77 students' essays about their experiences and ideals of assessment practices. We discuss how the students contributed to co-constructing the dominant status of exams in mathematics -- exams were deemed fit to assess mathematical knowledge. At the same time, experiences of alternative assessment practices enabled students to re-define what constitutes valid knowledge and how such knowledge can be demonstrated and assessed. We conclude by noting that developing student-centred assessment practices not only fosters students' learning but also promotes their epistemic resources.