test: ensure npm 7 E2E test reset global version back to the actual initial version

The `misc/npm-7` E2E test previously assumed the initial version of npm was 6.x and
would then always install 6.x after the test was complete. With newer Node.js versions
this assumption is no longer true. The test now records the initial version present
prior to starting the test and restores that recorded version at completion.

Author: clydin

tests/legacy-cli/e2e/tests/misc/npm-7.ts

@@ -1,3 +1,6 @@
+import * as assert from 'assert';
+import { execSync } from 'child_process';
+import { valid as validSemVer } from 'semver';
 import { rimraf } from '../../utils/fs';
 import { getActivePackageManager } from '../../utils/packages';
 import { ng, npm } from '../../utils/process';
@@ -17,6 +20,23 @@ export default async function () {
     return;
   }
 
+  // Get current package manager version to restore after tests
+  const initialVersionText = execSync('npm --version', {
+    encoding: 'utf8',
+    stdio: ['ignore', 'pipe', 'ignore'],
+    env: {
+      ...process.env,
+      //  NPM updater notifier will prevent the child process from closing until it timeouts after 3 minutes.
+      NO_UPDATE_NOTIFIER: '1',
+      NPM_CONFIG_UPDATE_NOTIFIER: 'false',
+    },
+  }).trim();
+  const initialVersion = validSemVer(initialVersionText);
+  assert.ok(
+    initialVersion,
+    `Invalid npm version string returned from "npm --version" [${initialVersionText}]`,
+  );
+
   const currentDirectory = process.cwd();
 
   const extraArgs = [];
@@ -89,7 +109,7 @@ export default async function () {
     // Change directory back
     process.chdir(currentDirectory);
 
-    // Reset version back to 6.x
-    await npm('install', '--global', 'npm@6');
+    // Reset version back to initial version
+    await npm('install', '--global', `npm@${initialVersion}`);
   }
 }