diff --git a/test/connection-state-recovery.ts b/test/connection-state-recovery.ts
index 9d205799..b9d1678c 100644
--- a/test/connection-state-recovery.ts
+++ b/test/connection-state-recovery.ts
@@ -222,11 +222,11 @@ describe("connection state recovery", () => {
 
     class DummyAdapter extends Adapter {
       override persistSession(session) {
-        expect.fail();
+        expect().fail();
       }
 
       override restoreSession(pid, offset) {
-        expect.fail();
+        expect().fail();
         return Promise.reject("should not happen");
       }
     }
diff --git a/test/messaging-many.ts b/test/messaging-many.ts
index 983ea236..ce710626 100644
--- a/test/messaging-many.ts
+++ b/test/messaging-many.ts
@@ -526,7 +526,7 @@ describe("messaging many", () => {
     ]).then(async () => {
       try {
         await io.timeout(200).emitWithAck("some event");
-        expect.fail();
+        expect().fail();
       } catch (err) {
         expect(err).to.be.an(Error);
         // @ts-ignore
diff --git a/test/socket-timeout.ts b/test/socket-timeout.ts
index 813ec9a2..62f36807 100644
--- a/test/socket-timeout.ts
+++ b/test/socket-timeout.ts
@@ -62,7 +62,7 @@ describe("timeout", () => {
     io.on("connection", async (socket) => {
       try {
         await socket.timeout(50).emitWithAck("unknown");
-        expect.fail();
+        expect().fail();
       } catch (err) {
         expect(err).to.be.an(Error);
         success(done, io, client);
diff --git a/test/support/expectjs.d.ts b/test/support/expectjs.d.ts
new file mode 100644
index 00000000..9774e1e4
--- /dev/null
+++ b/test/support/expectjs.d.ts
@@ -0,0 +1,221 @@
+declare function expect(target?: any): Expect.Root;
+
+declare namespace Expect {
+  interface Assertion {
+    /**
+     * Check if the value is truthy
+     */
+    ok(): void;
+
+    /**
+     * Creates an anonymous function which calls fn with arguments.
+     */
+    withArgs(...args: any[]): Root;
+
+    /**
+     * Assert that the function throws.
+     *
+     * @param fn callback to match error string against
+     */
+    throwError(fn?: (exception: any) => void): void;
+
+    /**
+     * Assert that the function throws.
+     *
+     * @param fn callback to match error string against
+     */
+    throwException(fn?: (exception: any) => void): void;
+
+    /**
+     * Assert that the function throws.
+     *
+     * @param regexp regexp to match error string against
+     */
+    throwError(regexp: RegExp): void;
+
+    /**
+     * Assert that the function throws.
+     *
+     * @param fn callback to match error string against
+     */
+    throwException(regexp: RegExp): void;
+
+    /**
+     * Checks if the array is empty.
+     */
+    empty(): Assertion;
+
+    /**
+     * Checks if the obj exactly equals another.
+     */
+    equal(obj: any): Assertion;
+
+    /**
+     * Checks if the obj sortof equals another.
+     */
+    eql(obj: any): Assertion;
+
+    /**
+     * Assert within start to finish (inclusive).
+     *
+     * @param start
+     * @param finish
+     */
+    within(start: number, finish: number): Assertion;
+
+    /**
+     * Assert typeof.
+     */
+    a(type: string): Assertion;
+
+    /**
+     * Assert instanceof.
+     */
+    a(type: Function): Assertion;
+
+    /**
+     * Assert typeof / instanceof.
+     */
+    an: An;
+
+    /**
+     * Assert numeric value above n.
+     */
+    greaterThan(n: number): Assertion;
+
+    /**
+     * Assert numeric value above n.
+     */
+    above(n: number): Assertion;
+
+    /**
+     * Assert numeric value below n.
+     */
+    lessThan(n: number): Assertion;
+
+    /**
+     * Assert numeric value below n.
+     */
+    below(n: number): Assertion;
+
+    /**
+     * Assert string value matches regexp.
+     *
+     * @param regexp
+     */
+    match(regexp: RegExp): Assertion;
+
+    /**
+     * Assert property "length" exists and has value of n.
+     *
+     * @param n
+     */
+    length(n: number): Assertion;
+
+    /**
+     * Assert property name exists, with optional val.
+     *
+     * @param name
+     * @param val
+     */
+    property(name: string, val?: any): Assertion;
+
+    /**
+     * Assert that string contains str.
+     */
+    contain(...strings: string[]): Assertion;
+    string(str: string): Assertion;
+
+    /**
+     * Assert that the array contains obj.
+     */
+    contain(...objs: any[]): Assertion;
+    string(obj: any): Assertion;
+
+    /**
+     * Assert exact keys or inclusion of keys by using the `.own` modifier.
+     */
+    key(keys: string[]): Assertion;
+    /**
+     * Assert exact keys or inclusion of keys by using the `.own` modifier.
+     */
+    key(...keys: string[]): Assertion;
+    /**
+     * Assert exact keys or inclusion of keys by using the `.own` modifier.
+     */
+    keys(keys: string[]): Assertion;
+    /**
+     * Assert exact keys or inclusion of keys by using the `.own` modifier.
+     */
+    keys(...keys: string[]): Assertion;
+
+    /**
+     * Assert a failure.
+     */
+    fail(message?: string): Assertion;
+  }
+
+  interface Root extends Assertion {
+    not: Not;
+    to: To;
+    only: Only;
+    have: Have;
+    be: Be;
+  }
+
+  interface Be extends Assertion {
+    /**
+     * Checks if the obj exactly equals another.
+     */
+    (obj: any): Assertion;
+
+    an: An;
+  }
+
+  interface An extends Assertion {
+    /**
+     * Assert typeof.
+     */
+    (type: string): Assertion;
+
+    /**
+     * Assert instanceof.
+     */
+    (type: Function): Assertion;
+  }
+
+  interface Not extends Expect.NotBase {
+    to: Expect.ToBase;
+  }
+
+  interface NotBase extends Assertion {
+    be: Be;
+    have: Have;
+    include: Assertion;
+    only: Only;
+  }
+
+  interface To extends Expect.ToBase {
+    not: Expect.NotBase;
+  }
+
+  interface ToBase extends Assertion {
+    be: Be;
+    have: Have;
+    include: Assertion;
+    only: Only;
+  }
+
+  interface Only extends Assertion {
+    have: Have;
+  }
+
+  interface Have extends Assertion {
+    own: Assertion;
+  }
+}
+
+declare module "expect.js" {
+  //@ts-ignore
+  export = expect;
+}
diff --git a/test/support/util.ts b/test/support/util.ts
index f44fedb4..ac78016f 100644
--- a/test/support/util.ts
+++ b/test/support/util.ts
@@ -1,3 +1,4 @@
+/// <reference types="./expectjs" />
 import type { Server } from "../..";
 import {
   io as ioc,