Self-testing allows for the characterization of quantum systems with minimal assumptions. Existing methods rely on quantum nonlocality, limiting their application to entangled systems. This research introduces a robust method for self-testing individual systems using contextuality, based on the Klyachko-Can-Binicioğlu-Shumovsky (KCBS) inequality for qutrits. A lower bound on the fidelity of the state and measurements is established, and the method is experimentally demonstrated using a single trapped <sup>40</sup>Ca<sup>+</sup> ion with random measurements and perfect detection efficiency.
