I'm working on a typescript project using node and jest. I need to test a function that can or can not modify a global variable. I need help resetting the global variable( a typescript Map) because once it has been modified by one test it remains set with the old value and the new test does work.
file1.ts
let impCache: Map<sint, string>
export function functionToTest(string, number){
doALotOfThings()
ChecksAndReturnExceptionEct()
if (!impCache){
AtSomePointCouldModify_impCache()
}
doMoreStuff()
}
file1.test.ts
describe('All tests'){
describe('this test1 never change impCache', ()=>{
it('does its works', () => {
assert('all_is_ok').tobe(string)
})
})
describe('this test2 never change impCache', ()=>{
it('does its works', () => {
assert('all_is_ok').tobe(string)
})
})
describe('this test3 changes impCache', ()=>{
it('does its works', () => {
assert('all_is_ok').tobe(string)
})
})
describe('this test4 changes impCache', ()=>{
it('does its works', () => {
assert('this always fail when run with all test but succeeds alone, because the cache was already set by the previous test ').tobe(string)
})
})
}
What can I do to clear the value impCache variable, so test4 does not see impCache value that has already been set by test3 ?
BR
The solution is to create a sandbox using jest.isolateModules
This is a fantastic solution to a complex scenario you see time and again in the real world.
Kudos to the jest team !!
As far as I can see you do not expose the cache nor any function that could clear it. If it were a Redis cache or something then you would be able to clear it with some endpoint, but if it's in-memory you can't do anything unless you expose such a utility. I'd suggest you do just that, for the purpose of the tests ... for example a function called clearCache. Then you can simply put this in your test suite:
beforeEach(clearCache);
It makes sense to run each test in a clean environment, using some mechanism like this, so that each is independent of other tests.