add tests for set command

PR-URL: #2354
Credit: @nlf
Close: #2354
Reviewed-by: @ruyadorno

Author: nlf

test/lib/set.js

@@ -0,0 +1,33 @@
+const { test } = require('tap')
+const requireInject = require('require-inject')
+
+let configArgs = null
+const npm = {
+  commands: {
+    config: (args, cb) => {
+      configArgs = args
+      return cb()
+    },
+  },
+}
+
+const set = requireInject('../../lib/set.js', {
+  '../../lib/npm.js': npm,
+})
+
+test('npm set - no args', t => {
+  return set([], (err) => {
+    t.match(err, /npm set/, 'prints usage')
+    t.end()
+  })
+})
+
+test('npm set', t => {
+  return set(['email', 'me@me.me'], (err) => {
+    if (err)
+      throw err
+
+    t.strictSame(configArgs, ['set', 'email', 'me@me.me'], 'passed the correct arguments to config')
+    t.end()
+  })
+})