Refactor test case InteractsCorrectlyWithFileInterfaces
in reference project for section 15 to match how it
looks in section 17 reference test case.
Add refactoring step to course text at the end of section 13 where we
refactor test case InteractsCorrectlyWithFileInterfaces
[Reference project section 13] Refactor test case
InteractsCorrectlyWithFileInterfaces to match course text
[Reference project section 14] Refactor test case
InteractsCorrectlyWithFileInterfaces to match course text