The test and the definition of what is measured are intimately linked. The level of construct validity is based on how well the theory works and how well the test measures the abstraction in question. Establishing construct validity is an ongoing process which continues as part of theory development. Construct validity is established by a pattern of findings, showing the relationship of what the test measures to other measurements and analyzing those for fit with the theory. Convergent and divergent evidence is utilized.
Convergent evidence is demonstration that the test measures what it is supposed to measure.
Divergent evidence shows that a test is unrelated to things that the theory says it is supposed to be unrelated to. A test should have both convergent and divergent evidence. For instance, we can expect that IQ scores will converge with verbal ability, grades in college, etc. And if IQ scores should not converge with hair color or ring size. Some contend construct validity is the general case, relevant to all psychological tests.