jestjs/jest · error · Error

${methodName}() method does not exist

Error message

${methodName}() method does not exist

What it means

Thrown by `SpyRegistry.spyOn` in spyRegistry.ts:100 when `obj[methodName] === void 0`. The host object exists but has no property by that name, so there is nothing to replace with a spy.

Source

Thrown at packages/jest-jasmine2/src/jasmine/spyRegistry.ts:100

    this.spyOn = (obj, methodName, accessType) => {
      if (accessType) {
        return this._spyOnProperty(obj, methodName, accessType);
      }

      if (obj === void 0) {
        throw new Error(
          getErrorMsg(
            `could not find an object to spy upon for ${methodName}()`,
          ),
        );
      }

      if (methodName === void 0) {
        throw new Error(getErrorMsg('No method name supplied'));
      }

      if (obj[methodName] === void 0) {
        throw new Error(getErrorMsg(`${methodName}() method does not exist`));
      }

      if (obj[methodName] && isSpy(obj[methodName])) {
        if (this.respy) {
          return obj[methodName];
        } else {
          throw new Error(
            getErrorMsg(`${methodName} has already been spied upon`),
          );
        }
      }

      let descriptor;
      try {
        descriptor = Object.getOwnPropertyDescriptor(obj, methodName);
      } catch {
        // IE 8 doesn't support `definePropery` on non-DOM nodes
      }

View on GitHub (pinned to f49721c78e)

Solutions

1. Verify the method name exists on the object: `console.log(typeof obj.methodName)`.
2. If the method is on the prototype, spy on the prototype: `spyOn(MyClass.prototype, 'method')`.
3. After a dependency upgrade, grep the new version for the method name to catch renames.

Example fix

// before
spyOn(userService, 'fetchUser')
// after
spyOn(userService, 'getUser')

if (typeof obj[methodName] !== 'function') { throw new Error(`${methodName} is not a method on obj`); }
spyOn(obj, methodName);

const hasMethod = (o: Record<string, any>, m: string): boolean =>
  typeof o?.[m] === 'function';

When it happens

Trigger: Calling `spyOn(userService, 'fetchUser')` when the method is actually named `getUser`; spying on an instance method that only exists on the prototype and the instance does not expose it; the method was renamed/removed in a library upgrade.

Common situations: Renaming a source method without updating tests; mocking a method that lives on a different object (class vs instance); version mismatch where the dependency dropped or renamed the API.

Related errors

• could not find an object to spy upon for ${methodName}()
• No method name supplied
• ${methodName} has already been spied upon
• ${methodName} is not declared writable or has no setter
• Spies must be created in a before function or a spec

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/ef7c631181a6ccec.json. Report an issue: GitHub.