simple test file takes about 40 seconds？

[pablezhang]

Issue :

The speed of ts-jest is too slow。
The cache is not valid, all files will be recomplied in watch mode.
A very simple test file takes about 40 seconds

Expected behavior :

1. faster speed
2. Test only modified files at a time in watch mode.

Minimal repo :

there are a minimal repo:https://github.com/pablezhang/react-app-unit-test

[ahnpnl]

We are trying to fix perf issue with #1049 but we need more help from community regarding to debug info to find out more perf causes

[ahnpnl]

Close as duplicate #1115, workaround in #1044 or use isolatedModule=true