[MM-47961] Migrate /support/assertions.js e2e tests file to TypeScript (#25731)

e2e-tests/cypress/tests/support/assertions.ts

@@ -0,0 +1,26 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+// Asserts that an item in the channel sidebar is not unread.
+export function beRead(items) {
+    expect(items).to.have.length(1);
+    expect(items[0].className).to.not.match(/unread-title/);
+}
+
+// Asserts that an item in the channel sidebar is read.
+export function beUnread(items) {
+    expect(items).to.have.length(1);
+    expect(items[0].className).to.match(/unread-title/);
+}
+
+// Asserts that an item in the channel sidebar is muted.
+export function beMuted(items) {
+    expect(items).to.have.length(1);
+    expect(items[0].className).to.match(/muted/);
+}
+
+// Asserts that an item in the channel sidebar is unmuted.
+export function beUnmuted(items) {
+    expect(items).to.have.length(1);
+    expect(items[0].className).to.not.match(/muted/);
+}