Revert "Revert "Factor out MessageEvent.from() usage (#9882)""

This reverts commit 99e38ca88e.

test/test-utils/events.ts

@@ -0,0 +1,42 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { MsgType } from "matrix-js-sdk/src/@types/event";
+
+interface MessageContent {
+    msgtype: MsgType;
+    body: string;
+    format?: string;
+    formatted_body?: string;
+}
+
+/**
+ * Creates the `content` for an `m.room.message` event based on input.
+ * @param text The text to put in the event.
+ * @param html Optional HTML to put in the event.
+ * @returns A complete `content` object for an `m.room.message` event.
+ */
+export function createMessageEventContent(text: string, html?: string): MessageContent {
+    const content: MessageContent = {
+        msgtype: MsgType.Text,
+        body: text,
+    };
+    if (html) {
+        content.format = "org.matrix.custom.html";
+        content.formatted_body = html;
+    }
+    return content;
+}