Were any scientific investigations conducted for proposing the theory? Was this theory tested or simply expected?

Yes

Explanation:

Scientific theory can be defined as the solutions to the problems of the queries related to natural phenomena or it is the explanation for different aspects of the natural world. It is done with repeated testing procedure. To prove the facts of the theory, repeated experimental tests, and observations are done. The theories are tested under the controlled conditions of the experimental set up.

On the basis of the above description, we can say that the scientific investigations are done in the form of experimentation trials before proposing  a theory. The theory is tested and is not simply expected.