Educational research has shown that self-beliefs can have profound influences on learning behaviour and achievement. It follows, then, that beliefs about the nature of programming aptitude (e.g., students' mindset) and the way in which individuals perceive themselves as programmers (e.g., students' self-concept) could also have a salient impact on programming practice behaviour and the development of programming expertise. However, in order to test this hypothesis, a valid and reliable measurement instrument is needed. This paper draws upon the Control-Value Theory of Achievement Emotion to assemble such a measurement instrument. An evaluation of the proposed measurement instrument with three cohorts of undergraduate computing students (N=239) then demonstrates that reliability and construct validity are adequate, while the concurrent validity of the conceptual framework is satisfactory. This suggests that the measurement instrument is suitable for further research into students' self-beliefs within the introductory programming context. However, it is important to note that this work represents only a first step and further validation is required to establish whether the measurement instrument is valid across different contexts and populations.