mockachai mongooseError
const mongooseError = (modelName, listPropertyError) => { const refectoredList = listPropertyError.reverse().map((elem) => { return " " + elem + ": Path `" + elem + "` is required."; }); return modelName + " validation failed:" + refectoredList.join(","); }; createStub.throws(new Error(mongooseError("Test", ["PropertyNameFromYourModel"]))); delete => expect(res).to.have.property("err"); if you have it and replace it with: expect(res.err.message).to.be.eq(mongooseError("Test", ["PropertyNameFromYourModel"])); expect(res.status).to.be.eq("error");