When using testbeds in the context of experimental computer science, the ability to produce trustworthy and reproducible experiments results depends greatly on the trustworthiness of the infrastructure itself. Unfortunately, several factors many issues such as software misconfiguration, hardware heterogeneity, or service failures, can remain undetected and affect the quality of experimental results. This paper presents the design and implementation of an automated testbed testing framework. This framework was deployed in the context of the Grid'5000 project, and uncovered more than one hundred of issues. (see also https://hal.inria.fr/hal-01538682 for an extended version of this work)