LoginPage.java

package org.demo.ui;

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;

public class LoginPage {

    private final WebDriver driver;

    public LoginPage(WebDriver driver) {
        this.driver = driver;
    }

    public void open() {
        driver.get("https://www.saucedemo.com/");
    }

    public void login(String user, String pass) {
        driver.findElement(By.id("user-name")).sendKeys(user);
        driver.findElement(By.id("password")).sendKeys(pass);
        driver.findElement(By.id("login-button")).click();
    }

    public boolean isErrorVisible() {
        return !driver.findElements(By.cssSelector("[data-test='error']")).isEmpty();
    }

}