[SalesForce] npm command not found when working with jest in LWC

You were pretty much spot on with your investigation and finding that lwc-jest has been deprecated in favor of sfdx-lwc-jest. The SFDX plugin was in fact referencing the deprecated binary.

This has just been fixed in the plugin by this PR and should be released into the main SFDX CLI via a patch release in a week or two.

Use the command npm run test:unit:coverage (i.e., usage of flag --coverage in your test command or you may even update this in the scripts section of package.json config/ you may be familiar with this approach if you have worked in node or npm).

--Update-(Start)--:

Add the following to the package.json, if you don't have it already.

"scripts": {
    "test": "npm run test:unit",
    "test:unit": "sfdx-lwc-jest",
    "test:unit:watch": "sfdx-lwc-jest --watch",
    "test:unit:debug": "sfdx-lwc-jest --debug",
    "test:unit:coverage": "sfdx-lwc-jest --coverage"
  }

--Update-(End)--:

[Or, you can configure the jest.config.js file for various coverage options as mentioned here. Note: I've personally not tested using these config options but it should be possible].

See the screenshot below for the percentage covered information in table format. The last column Uncovered Line #s shows the lines that were not covered in the unit test. This isn't similar to way it shows up for apex in Dev Console, but gets you the required information.