Jest leaks memory allocating strings for imported files

I'm trying to understand why my jest tests are leaking memory but I've not idea what can be the cause. Looks like jest allocates a huge amount of strings (seems the imports) but I don't understand why they do that.

I start the tests disabling module cache:

node --inspect-brk --expose-gc ./node_modules/.bin/jest --runInBand --logHeapUsage --no-cache

and I get the following output: as you see, there are tons of MB allocated for module contents.

Any idea how can I try to reduce that amount of memory?