Properly set npm_command environment variable.

Fix: #2015

PR-URL: #2016
Credit: @isaacs
Close: #2016
Reviewed-by: @ruyadorno

lib/npm.js

@@ -93,7 +93,12 @@ const npm = module.exports = new class extends EventEmitter {
     }
 
     process.emit('time', `command:${cmd}`)
-    this.command = cmd
+    // since 'test', 'start', 'stop', etc. commands re-enter this function
+    // to call the run-script command, we need to only set it one time.
+    if (!this.command) {
+      process.env.npm_command = cmd
+      this.command = cmd
+    }
 
     // Options are prefixed by a hyphen-minus (-, \u2d).
     // Other dash-type chars look similar but are invalid.
@@ -142,7 +147,6 @@ const npm = module.exports = new class extends EventEmitter {
       }
       if (!er && !this[_flatOptions]) {
         this[_flatOptions] = require('./utils/flat-options.js')(this)
-        process.env.npm_command = this.command
       }
       process.emit('timeEnd', 'npm:load')
       this.emit('load', er)

test/lib/npm.js

@@ -4,7 +4,16 @@ const fs = require('fs')
 
 // delete this so that we don't have configs from the fact that it
 // is being run by 'npm test'
+const event = process.env.npm_lifecycle_event
 for (const env of Object.keys(process.env).filter(e => /^npm_/.test(e))) {
+  if (env === 'npm_command') {
+    // should only be running this in the 'test' or 'run-script' command!
+    // if the lifecycle event is 'test', then it'll be 'test', otherwise
+    // it should always be run-script.  Of course, it'll be missing if this
+    // test is just run directly, which is also acceptable.
+    const cmd = event === 'test' ? 'test' : 'run-script'
+    t.match(process.env[env], cmd)
+  }
   delete process.env[env]
 }