Adds tests accidentally removed in #4305

Author: arcanis

packages/yarnpkg-core/tests/Configuration.test.ts

@@ -1,7 +1,7 @@
-import {xfs, PortablePath}     from '@yarnpkg/fslib';
-import NpmPlugin               from '@yarnpkg/plugin-npm';
+import {xfs, PortablePath}                 from '@yarnpkg/fslib';
+import NpmPlugin                           from '@yarnpkg/plugin-npm';
 
-import {Configuration, SECRET} from '../sources/Configuration';
+import {Configuration, SECRET, TAG_REGEXP} from '../sources/Configuration';
 
 async function initializeConfiguration<T>(value: {[key: string]: any}, cb: (dir: PortablePath) => Promise<T>) {
   return await xfs.mktempPromise(async dir => {
@@ -11,6 +11,20 @@ async function initializeConfiguration<T>(value: {[key: string]: any}, cb: (dir:
   });
 }
 
+describe(`TAG_REGEXP`, () => {
+  const validTags = [
+    `canary`,
+    `latest`,
+    `next`,
+    `legacy_v1`,
+  ];
+
+  it(`should allow all valid tags`, () => {
+    const badTags = validTags.filter(tag => !TAG_REGEXP.test(tag));
+    expect(badTags.length).toBe(0);
+  });
+});
+
 describe(`Configuration`, () => {
   it(`should hide secrets`, async () => {
     await initializeConfiguration({