Lectures are way ahead of the planned schedule for the course. What should be done? In my university, we submit a lecture plan at the academic semester starts. The lecture plan is a kind of semi-official documentation on the schedule of lectures or topics (Ref: Planning a course: lecture-by-lecture or topic-by-topic?). The lecture plan looks like the following that also includes the plan for quizzes, tests, projects.

--------------------------------------------
Week    Topic      Subtopics     Expectation
--------------------------------------------
W01     Topic1     St1, St2      To achieve.
W02     Topic1     St3, St4      ---
...some weeks of such lecturing...
Quiz1 ...
W07     Topic7     St1, St2      ---
W08     Topic8     St1, St2      ---
...and some more...
Mid-way Test
...Again lecturing...
Project
Final test
---------------------------------------------


Now I am in a problem. The mid-way test has been scheduled in next 3 weeks. But, I have completed all the stuff required for the mid-way test. I don't have any more things to lecture and I don't want to.

Should I complete the course well before time? But, again my dean might not be happy with this.

Or, what should one lecturer do in such a scenario? 

Suggestion with some experiences would be really appreciated.

P.S. This is undergrad course if at all it matters.
Generally, when a course is assigned a certain number of credit hours, that means that students (and professors) can expect a related number of contact-hours via lecture, tutorials or labs. Your students and dean will likely be upset if you cancel classes for next 3 weeks. 

If you don't want to introduce new material, there are several things you could do.


Review material or go further into depth 
Have students work on their projects 
Have students work on homework or small projects