Assessing competences always poses a challenge and can be even more complicated when tackling a multidimensional competence like teacher digital competence (TDC). TDC is understood to consist of different dimensions linked to its components. This complexity gives rise to the need to organize and systematize both TDC training and its evaluation through a standard based on validated benchmark indicators. Designing and developing an instrument for TDC assessment has been a two-phase process. The COMDID-A self-assessment tool was developed in the first phase and COMDID-C, an instrument for assessing knowledge related to TDC, in the second. In this article we present the process of constructing the COMDID-C instrument. For this first stage, we worked with two samples, an expert validation and a pilot test sample. Due to the complexity of the test, we conducted a preliminary evaluation of the validity of its content, construction and reliability. Our results indicate that the test is well designed and consistent with its intended purpose. The next step will be administering the test to a larger sample that will allow the instrument to be externally validated.