gistfile1.txt

export class LoginForm {

    private readonly logInButton = element(With.id('sub'));

    async login(username: string, password: string) {
        await this.setLogin(username);
        await this.setPassword(password);
        await this.submit();
        const mainpage = new MainPage();
        await mainpage.shouldBeOpened()
        return mainpage;    
    }

    async setLogin(username = 'username'): Promise<void> {
        await element('#txtUserID').setValue(username);
    }

    async setPassword(password = 'password'): Promise<void> {
        await element('#txtPassword').setValue(password);
    }

    async submit(): Promise<void> {
        await this.logInButton.click();
    }
      
     async errorMessageShouldBe(text: string) {
      ...
     }
}