diff --git a/test/topics/crossposts.js b/test/topics/crossposts.js
new file mode 100644
index 0000000000..809821f97e
--- /dev/null
+++ b/test/topics/crossposts.js
@@ -0,0 +1,160 @@
+'use strict';
+
+const assert = require('assert');
+
+const db = require('../mocks/databasemock');
+
+const user = require('../../src/user');
+const categories = require('../../src/categories');
+const topics = require('../../src/topics');
+const utils = require('../../src/utils');
+
+describe('Crossposting (& related logic)', () => {
+	describe('topic already in multiple categories', () => {
+		let tid;
+		let cid1;
+		let cid2;
+		let uid;
+
+		before(async () => {
+			({ cid: cid1 } = await categories.create({ name: utils.generateUUID().slice(0, 8) }));
+			uid = await user.create({ username: utils.generateUUID().slice(0, 8) });
+			const { topicData } = await topics.post({
+				uid,
+				cid: cid1,
+				title: utils.generateUUID(),
+				content: utils.generateUUID(),
+			});
+			tid = topicData.tid;
+
+			// Add topic to another category's zset
+			const crosspostCategory = await categories.create({ name: utils.generateUUID().slice(0, 8) });
+			cid2 = crosspostCategory.cid;
+			await db.sortedSetAdd(`cid:${crosspostCategory.cid}:tids`, topicData.timestamp, tid);
+		});
+
+		it('should contain the topic in both categories when requested', async () => {
+			const tids1 = await categories.getTopicIds({
+				uid,
+				cid: cid1,
+				start: 0,
+				stop: 1,
+			});
+
+			const tids2 = await categories.getTopicIds({
+				uid,
+				cid: cid2,
+				start: 0,
+				stop: 1,
+			});
+
+			assert.deepStrictEqual(tids1, tids2);
+		});
+	});
+
+	describe('crosspost', () => {
+		let tid;
+		let cid1;
+		let cid2;
+		let uid;
+
+		before(async () => {
+			({ cid: cid1 } = await categories.create({ name: utils.generateUUID().slice(0, 8) }));
+			const crosspostCategory = await categories.create({ name: utils.generateUUID().slice(0, 8) });
+			cid2 = crosspostCategory.cid;
+			uid = await user.create({ username: utils.generateUUID().slice(0, 8) });
+			const { topicData } = await topics.post({
+				uid,
+				cid: cid1,
+				title: utils.generateUUID(),
+				content: utils.generateUUID(),
+			});
+			tid = topicData.tid;
+		});
+
+		it('should successfully crosspost to another cid', async () => {
+			const crossposts = await topics.tools.crosspost(tid, cid2, uid);
+
+			assert(Array.isArray(crossposts));
+			assert.strictEqual(crossposts.length, 1);
+			assert.partialDeepStrictEqual(crossposts[0], {
+				uid,
+				tid,
+				cid: cid2,
+			});
+		});
+
+		it('should show the tid in both categories when requested', async () => {
+			const tids1 = await categories.getTopicIds({
+				uid,
+				cid: cid1,
+				start: 0,
+				stop: 1,
+			});
+
+			const tids2 = await categories.getTopicIds({
+				uid,
+				cid: cid2,
+				start: 0,
+				stop: 1,
+			});
+
+			assert.deepStrictEqual(tids1, tids2);
+		});
+
+		it('should throw on cross-posting again when already cross-posted', async () => {
+			await assert.rejects(
+				topics.tools.crosspost(tid, cid2, uid),
+				{ message: '[[error:topic-already-crossposted]]' },
+			);
+		});
+	});
+
+	describe('uncrosspost', () => {
+		let tid;
+		let cid1;
+		let cid2;
+		let uid;
+
+		before(async () => {
+			({ cid: cid1 } = await categories.create({ name: utils.generateUUID().slice(0, 8) }));
+			const crosspostCategory = await categories.create({ name: utils.generateUUID().slice(0, 8) });
+			cid2 = crosspostCategory.cid;
+			uid = await user.create({ username: utils.generateUUID().slice(0, 8) });
+			const { topicData } = await topics.post({
+				uid,
+				cid: cid1,
+				title: utils.generateUUID(),
+				content: utils.generateUUID(),
+			});
+			tid = topicData.tid;
+
+			await topics.tools.crosspost(tid, cid2, uid);
+		});
+
+		it('should successfully uncrosspost from a cid', async () => {
+			const crossposts = await topics.tools.uncrosspost(tid, cid2, uid);
+
+			assert(Array.isArray(crossposts));
+			assert.strictEqual(crossposts.length, 0);
+		});
+
+		it('should not contain the topic in the category the topic was uncrossposted from', async () => {
+			const tids = await categories.getTopicIds({
+				uid,
+				cid: cid2,
+				start: 0,
+				stop: 1,
+			});
+
+			assert(!tids.includes(tid));
+		});
+
+		it('should throw on uncrossposting if already uncrossposted', async () => {
+			assert.rejects(
+				topics.tools.uncrosspost(tid, cid2, uid),
+				'[[error:invalid-data]]',
+			);
+		});
+	});
+});
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