Purpose of the study: To collect validity evidence for the chest tube insertion (CTI) test mode on the medical simulation application Touch Surgery. This was done by using Messick's contemporary framework. Methods: Novice, intermediate and experienced participants provided informed consent and demographic information. After familiarisation with the application, they completed the CTI test mode. Validity evidence was collected from four sources: content, response process, relation to other variables and consequences. A post-study questionnaire with 5-point Likert scales assessed the perceived realism, relevance and utility of the assessment. Mean scores of the three groups were compared. Results: A total of 25 novices, 11 intermediates and 19 experienced participants were recruited. Content evidence was collected by an expert in CTI and was based on published literature and guidelines. All users were familiarised with the application, and received standardised instructions throughout the test. Most users rated the simulation as realistic and suitable to assess cognitive skills. Novices received significantly lower (55.9±7.5) test mode scores than intermediates (80.6±4.4) (p<0.001) and experienced participants (82.3±5.3) (p<0.001). There was no significant difference in score between intermediate and experienced participants (p=0.75). Consequences evidence was provided by establishing a pass/fail score of 71% using the contrasting groups method, which resulted in one observed false positive and no false negatives. Conclusion: A robust validity argument was constructed for the CTI test mode, which can be implemented in surgical curricula to assess learners' cognitive skills prior to hands-on simulation practice.