diff --git a/backend/app/templates/mail_sources.html b/backend/app/templates/mail_sources.html
index e821228..40da181 100644
--- a/backend/app/templates/mail_sources.html
+++ b/backend/app/templates/mail_sources.html
@@ -454,7 +454,7 @@ function mailSourcesApp() {
         },
 
         async testSource(id) {
-            this.$set(this.testing, id, true);
+            this.testing[id] = true;
             this.feedback = { message: '', type: '' };
             try {
                 const resp = await fetch(`/api/v1/mail-sources/${id}/test`, { method: 'POST' });
@@ -474,7 +474,7 @@ function mailSourcesApp() {
             } catch (e) {
                 this.feedback = { message: `Test error: ${e.message}`, type: 'error' };
             } finally {
-                this.$set(this.testing, id, false);
+                this.testing[id] = false;
             }
         },
 
diff --git a/backend/app/tests/test_mail_sources.py b/backend/app/tests/test_mail_sources.py
index 511d157..0814670 100644
--- a/backend/app/tests/test_mail_sources.py
+++ b/backend/app/tests/test_mail_sources.py
@@ -147,9 +147,7 @@ class TestMailSourcesAPI:
         db_session.add(MailSource(name="Disabled", method="IMAP", enabled=False))
         db_session.commit()
 
-        enabled = (
-            db_session.query(MailSource).filter(MailSource.enabled == True).all()  # noqa: E712
-        )
+        enabled = db_session.query(MailSource).filter(MailSource.enabled).all()
         assert len(enabled) == 2
         names = {s.name for s in enabled}
         assert "Enabled A" in names