allow runner to use custom shell

[connectdotz]

motivation

We used to launch jest process with the default shell defined by Node child_process, however, there are issues like jest-community/vscode-jest#708 that would have worked in a different shell (powershell). There are also a few shell environment-related issues that could also benefit from specifying the same shell users actually use.

Also removed the CI: true flag in the process.env as a workaround in the past. Now, this is better served by adding an explicit jest argument --watchAll=false if needed. However since this could be a breaking change, we should cust a major release to be safe.

summary

• added shell option in ProjectWorkspace
• remove CI: true flag in the runner env override. Projects can pass explicit watchAll=false to ensure the same effect if needed.

[connectdotz]

@stephtr if you have some cycle, could you try setting shell to powershell in windows to make sure it worked as expected? thanks.

[connectdotz]

@stephtr looks like you are busy. I will merge and address issues if any.