Test Driven Develpment Issues in refactoring

I am practicing with the Kata minesWeesper, an in the development of the code i have introduce a Class that parses the file.
When that Class parses and find a pair of numbers valid (see kata doc) it returns that pair.
First i was coding that pair as int[2], in order to make an extract class refactoring when the code was write, so my methods like getNextDimensions() returns a int[2].
I wrote the test in Junit and in order to check the answer i had compared to a new int[2]= [expectedResultLines,expecterResulColumns].
Once all my test pass, i began to refactor code. (this could be a point of my error, but not the clue), when i did the refactor, i created a class MapDimensions , which stores the dimensions of the map in two variables.
And now a find me changing all the test and the clients of my class.

How i could avoid that mistake?

I don't know just now but i can expose some clues.
SMELL.- test comparing primitive results.--> change to a class container.
think also to use encapsulate field
Good practice --> introduce name of the expected type of answer in test name
introduce "expected" word in the declaration of the expected result to mach in the test.