Which type of investigations include a hypothesis?

The experimental type of investigation tests the proposed hypothesis.  

Explanation:

There are mainly three types of investigation in a research namely,  experimental investigation, comparative investigations and the descriptive investigations. Of the three, hypothesis is proposed in experimental type of investigation in research. There are two hypothesis given, one is null hypothesis and other is alternate hypothesis.

The hypothesis is tested with experimentation and when the results proves the hypothesis the theory is accepted. And later that may be formulated into law or meets the research objectives.