This is the section of my VS Code User Preferences settings.json (to access, Ctrl +P then select Preferences: Open User Settings) for Jest VS Code extension:

{
    ...
    "jest.coverageFormatter": "GutterFormatter",  
    "jest.debugCodeLens.showWhenTestStateIn": [
        "fail",
        "unknown",
        "pass",
        "skip"
    ]
}

I found that the Jest extension's Debug CodeLens wouldn't always appear on tests. A lot of the time I had to go to Testing window in VS Code sidebar to start debugging on a test because the Debug codelens wasn't available on the test in situ in the code file.

Turns out this was because jest.debugCodeLens.showWhenTestStateIn has default value of ["fail", "unknown"].

I added the other two possible statuses to ensure that the Debug codelens is always available.

The other setting here is jest.coverageFormatter. I find seeing coverage in the gutter on the left of a file unobtrusive compared to the extension's default behaviour of colour-coding regions of code in the file.

You can of course set the above on a per project basis by putting the snippet above in .vscode\settings.json in your workspace (this file can be created/navigated to using the command Ctrl + P then Preferences: Open Workspace Settings).