add a test to make sure the targets in package.json are well formatted

ts/test/session/unit/updater/updater_test.ts

@@ -1,4 +1,20 @@
+import { readFileSync } from 'fs-extra';
+import { isEmpty } from 'lodash';
+import path from 'path';
+
 describe('Updater', () => {
   // tslint:disable-next-line: no-empty
   it.skip('isUpdateAvailable', () => {});
+
+  it('package.json target are correct', () => {
+    const content = readFileSync(
+      path.join(__dirname, '..', '..', '..', '..', '..', 'package.json')
+    );
+
+    if (!content || isEmpty(content) || !content.includes('"target": ["deb", "rpm", "freebsd"],')) {
+      throw new Error(
+        'Content empty or does not contain the target on a single line. They have to be for the linux appImage build to pass.'
+      );
+    }
+  });
 });