Use a mock filesystem for testing

[Klock85]

The tests in my PR (#68) write test files to the filesystem and remove them after tests are complete.

I am sure there is a way to do this using a mocked filesystem instead which may be less resource intensive in terms of reads and writes?

[devlopersabbir]

Check this pull request #65
I think we should use like way our code. Because index.ts file is not fully readable...

Note please check this PR and update me... :)