diff --git a/frontend/test-client/src/agent/mock-agent.ts b/frontend/test-client/src/agent/mock-agent.ts
index ff70520..23fcd09 100644
--- a/frontend/test-client/src/agent/mock-agent.ts
+++ b/frontend/test-client/src/agent/mock-agent.ts
@@ -25,23 +25,24 @@ export class MockAgent extends MockClient {
 	}
 
 	public async init(): Promise<void> {
-		await super.init();
+		await super.init(
+			// flaky fetch implementation to use during testing
+			async (
+				input: string | URL | globalThis.Request,
+				init?: RequestInit
+			): Promise<Response> => {
+				await sleep(Math.random() * this.jitterScaleInSeconds * 1000);
+				const response = await fetch(input, init);
+				await sleep(Math.random() * this.jitterScaleInSeconds * 1000);
+				return response;
+			}
+		);
 
 		assert(
 			(await this.client.checkConnection()).isSuccessful,
 			"Connection check failed"
 		);
 
-		this.client.fetchImplementation = async (
-			input: string | URL | globalThis.Request,
-			init?: RequestInit
-		): Promise<Response> => {
-			await sleep(Math.random() * this.jitterScaleInSeconds * 1000);
-			const response = await fetch(input, init);
-			await sleep(Math.random() * this.jitterScaleInSeconds * 1000);
-			return response;
-		};
-
 		this.client.logger.addOnMessageListener((logLine: LogLine) => {
 			const state = this.client.getSettings().isSyncEnabled
 				? "(online) "
diff --git a/frontend/test-client/src/agent/mock-client.ts b/frontend/test-client/src/agent/mock-client.ts
index 1adae4b..9d4d457 100644
--- a/frontend/test-client/src/agent/mock-client.ts
+++ b/frontend/test-client/src/agent/mock-client.ts
@@ -16,11 +16,17 @@ export class MockClient implements FileSystemOperations {
 		protected readonly useSlowFileEvents: boolean
 	) {}
 
-	public async init(): Promise<void> {
-		this.client = await SyncClient.create(this, {
-			load: async () => this.data,
-			save: async (data) => void (this.data = data)
-		});
+	public async init(
+		fetchImplementation: typeof globalThis.fetch
+	): Promise<void> {
+		this.client = await SyncClient.create(
+			this,
+			{
+				load: async () => this.data,
+				save: async (data) => void (this.data = data)
+			},
+			fetchImplementation
+		);
 
 		await Promise.all(
 			Object.keys(this.initialSettings).map(async (key) => {