fix(init): write package.json workspaces paths with / separators

This also refactors the test to use `mockNpm`

lib/commands/init.js

@@ -10,6 +10,8 @@ const PackageJson = require('@npmcli/package-json')
 const log = require('../utils/log-shim.js')
 const updateWorkspaces = require('../workspaces/update-workspaces.js')
 
+const posixPath = p => p.split('\\').join('/')
+
 const BaseCommand = require('../base-command.js')
 
 class Init extends BaseCommand {
@@ -203,7 +205,7 @@ class Init extends BaseCommand {
     pkgJson.update({
       workspaces: [
         ...(pkgJson.content.workspaces || []),
-        relative(this.npm.localPrefix, workspacePath),
+        posixPath(relative(this.npm.localPrefix, workspacePath)),
       ],
     })
 

tap-snapshots/test/lib/commands/init.js.test.cjs

@@ -5,30 +5,25 @@
  * Make sure to inspect the output below.  Do not ignore changes!
  */
 'use strict'
-exports[`test/lib/commands/init.js TAP npm init workspces with root > does not print helper info 1`] = `
-Array []
-`
+exports[`test/lib/commands/init.js TAP displays output > displays helper info 1`] = `
+This utility will walk you through creating a package.json file.
+It only covers the most common items, and tries to guess sensible defaults.
 
-exports[`test/lib/commands/init.js TAP workspaces no args > should print helper info 1`] = `
-Array []
-`
+See \`npm help init\` for definitive documentation on these fields
+and exactly what they do.
+
+Use \`npm install <pkg>\` afterwards to install a package and
+save it as a dependency in the package.json file.
 
-exports[`test/lib/commands/init.js TAP workspaces no args, existing folder > should print helper info 1`] = `
-Array []
+Press ^C at any time to quit.
 `
 
-exports[`test/lib/commands/init.js TAP workspaces post workspace-init reify > should print helper info 1`] = `
-Array [
-  Array [
-    String(
-      
-      added 1 package in 100ms
-    ),
-  ],
-]
+exports[`test/lib/commands/init.js TAP workspaces no args -- yes > should print helper info 1`] = `
+
+added 1 package in {TIME}
 `
 
-exports[`test/lib/commands/init.js TAP workspaces post workspace-init reify > should reify tree on init ws complete 1`] = `
+exports[`test/lib/commands/init.js TAP workspaces no args -- yes > should reify tree on init ws complete 1`] = `
 {
   "name": "top-level",
   "lockfileVersion": 3,
@@ -53,7 +48,3 @@ exports[`test/lib/commands/init.js TAP workspaces post workspace-init reify > sh
 }
 
 `
-
-exports[`test/lib/commands/init.js TAP workspaces with arg but missing workspace folder > should print helper info 1`] = `
-Array []
-`