I don’t think this might cover all test scenario’s even if you pass through all pieces of code. A branch on a variable would have worked fine with a right value, and the same can lead to an exception with a ‘null’ value and the result of this null might be based on the previous statement. I see the probabilities are more if you want to test each and every scenario.
Eg., a 3 step service can lead to 9 scenarios. 0-0-0, 0-0-1,… to 1-1-1. Testing just last scenario 1-1-1 cannot give an assurance that all the other 8 scenario’s would work.
In general, breaking the larger piece of code to smaller units of flow services would help a lot for re-usability, debugging, fixing, testing etc.,
My 2 cents.