Testing in the active sense is the most common way to performverification and validation of systems, but testing in the passivesense has one compelling property: independence. Independencefrom test stimuli and other passive tests opens up for parallel testingand off-line analysis. However, the tests can be difficult to developsince the complete testable state must be expressed using someformalism. We argue that a carefully chosen language togetherwith an interactive work flow, providing immediate feedback, canenable testers to approach passive testing. We have conducted a casestudy in the automotive domain, interviewing experienced testers.The testers have been introduced to, and had hands-on practicewith a tool. The tool is based on Easy Approach to RequirementsSyntax (EARS) and provides an interactive work flow for developingand evaluating test results. The case study shows that i) the testersbelieve passive testing is useful for many of their tests, ii) they seebenefits in parallelism and off-line analysis, iii) the interactive workflow is necessary for writing the testable state expression, but iv)when the testable state becomes too complex, then the proposedlanguage is a limitation. However, the language contributes toconcise tests, resembling executable requirements.