refactor: add destroy method (for testing) for backend transport

Additionally fix minor issues and refactor the class

src/notification/backend-transport.ts

@@ -13,6 +13,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
+import {Logger} from '@openstapps/logger';
 import {SMTP} from '@openstapps/logger/lib/smtp';
 import {Transport, VerifiableTransport} from '@openstapps/logger/lib/transport';
 
@@ -39,7 +40,7 @@ export class BackendTransport {
   /**
    * Stores information if transport is in state of waiting for the verification
    */
-  private readonly waitingForVerification: boolean;
+  private waitingForVerification = false;
 
   /**
    * A (SMTP) transport which includes settings for sending mails
@@ -47,16 +48,30 @@ export class BackendTransport {
   protected transport: SMTP | undefined;
 
   /**
-   * Provides an instance of a transport
+   * Destroys the singleton instance of the class (for unit test purposes)
    */
-  public static getTransportInstance(): SMTP | undefined {
+  public static destroy() {
+    delete BackendTransport._instance;
+  }
+
+  /**
+   * Provides instance of a backend transport
+   */
+  public static getInstance(): BackendTransport {
     if (typeof BackendTransport._instance !== 'undefined') {
-      return BackendTransport._instance.transport;
+      return BackendTransport._instance;
     }
 
     BackendTransport._instance = new BackendTransport();
 
-    return BackendTransport._instance.transport;
+    return BackendTransport._instance;
+  }
+
+  /**
+   * Provides an instance of a transport
+   */
+  public static getTransportInstance(): SMTP | undefined {
+    return BackendTransport.getInstance().transport;
   }
 
   private constructor() {
@@ -67,27 +82,30 @@ export class BackendTransport {
       this.transport = SMTP.getInstance();
     } catch (error) {
       if (process.env.ALLOW_NO_TRANSPORT === 'true') {
-        /* tslint:disable-next-line:no-console */
-        console.warn('SMTP error was ignored.');
+        Logger.warn('SMTP error was ignored.');
       } else {
         throw error;
       }
     }
 
     if (typeof this.transport !== 'undefined' && isTransportWithVerification(this.transport)) {
-      this.waitingForVerification = true;
+      void this.verifyTransport(this.transport);
+    }
+  }
 
-      this.transport.verify()
-        .then((message) => {
-          if (typeof message === 'string') {
-            // tslint:disable-next-line:no-console
-            console.log(message);
-          }
-        })
-        .catch((err) => {
-          throw err;
-        });
-    } else {
+  /**
+   * Verifies the transport using its verification method
+   */
+  private async verifyTransport(transport: VerifiableTransport): Promise<void> {
+    this.waitingForVerification = true;
+    try {
+      const successful = await transport.verify();
+      if (successful) {
+        Logger.log('SMTP verification successful.');
+      }
+    } catch (err) {
+      throw err;
+    } finally {
       this.waitingForVerification = false;
     }
   }