Assessments differ in what they measure and how closely they mirror the job. A work sample, such as drafting a reply to a customer complaint, tests a task directly, while a cognitive test measures general reasoning and a personality questionnaire looks at preferences and working style. They can be used at screening, alongside interviews or late in the process, and each should map to a requirement agreed for the role.
A well-chosen assessment gives evidence that a CV or conversation cannot, but each one adds time for the candidate and can affect who completes the process. Good practice is to use only assessments that test something the job needs, check pass rates across groups for adverse impact, offer reasonable adjustments and treat results as one input into a human decision rather than a verdict.