Dev mode with file watching

[eric-burel]

Is your feature request related to a problem? Please describe. There is no dev mode so we must manually rebuild. Describe the solution you'd like yarn run dev should run the build system in watch mode, in order to rebuild relevant package on change Describe alternatives you've considered Check Lerna documentation for how we can do that, or existing Lerna project like Babel, Jest...

[Apollinaire]

Because of the diverse types of packages we are going to host in this monorepo, we probably won't have one way of running them in dev. A "generic" option that would also bring a good practice is to use jest -w as a way to develop, this way the tests will be written with the features, and it will probably be good to maintain them as well. I don't know how lerna can cause problems with Jest though

[eric-burel]

The most common issue I have is when I edit package A, and I notice I need a change in package B => I need to rebuild package B for it to work correctly in package A. I don't actually need to rebuild the package I am actively developing to run the unit test because Jest do it correctly, only the package that I depend on.

So I think the most helpful thing we be to rerun yarn build for current package when a .ts/.tsx file is edited, we don't need a very advanced solution indeed.