Euclide is a new Constraint-Based Testing tool for verifying safety-critical C programs. By using a mixture of symbolic and numerical analyses (namely static single assignment form, constraint propagation, integer linear relaxation and search-based test data generation), it addresses three distinct applications in a single framework: structural test data generation, counter-example generation and partial program proving. This paper presents the main capabilities of the tool and relates an experience we had when verifying safety properties for a well-known critical C component of the TCAS (Traffic Collision Avoidance System). Thanks to Euclide, we found an unrevealed counter-example to a given anti-collision property.