A test showing an issue with Selenium's Keys.COMMAND.

SeleniumCommandIssue.java

import org.hamcrest.Matchers;
import org.junit.After;
import org.junit.Assert;
import org.junit.Rule;
import org.junit.Test;
import org.openqa.selenium.By;
import org.openqa.selenium.Keys;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.chrome.ChromeOptions;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.interactions.Actions;

import static org.hamcrest.Matchers.*;
import static org.junit.Assert.*;

public class SeleniumCommandIssue {

    private WebDriver driver;

    @After
    public void after() {
        driver.quit();
    }

    @Test
    public void workingWithFF() throws Exception {
        driver = new FirefoxDriver();

        driver.get("http://google.it");
        driver.findElement(By.name("q")).sendKeys("asd");
        Thread.sleep(1000);
        driver.findElement(By.name("q")).sendKeys(Keys.chord(Keys.COMMAND, "a"));
        Thread.sleep(1000);
        driver.findElement(By.name("q")).sendKeys("dsa");

        assertThat(driver.findElement(By.name("q")).getAttribute("value"),
                equalTo("dsa"));
    }

    @Test
    public void failingWithChrome1() throws Exception {
        driver = new ChromeDriver(new ChromeOptions().setHeadless(true));

        driver.get("http://google.it");
        driver.findElement(By.name("q")).sendKeys("asd");
        Thread.sleep(1000);
        driver.findElement(By.name("q")).sendKeys(Keys.chord(Keys.COMMAND + "a"));
        Thread.sleep(1000);
        driver.findElement(By.name("q")).sendKeys("dsa");
        assertThat(driver.findElement(By.name("q")).getAttribute("value"),
                equalTo("dsa"));
    }

    @Test
    public void failingWithChrome2() throws Exception {
        driver = new ChromeDriver(new ChromeOptions().setHeadless(true));

        driver.get("http://google.it");
        driver.findElement(By.name("q")).sendKeys("asd");
        Thread.sleep(1000);
        new Actions(driver)
                .keyDown(Keys.COMMAND)
                .sendKeys("a")
                .keyUp(Keys.COMMAND)
                .perform();
        Thread.sleep(1000);
        driver.findElement(By.name("q")).sendKeys("dsa");
        assertThat(driver.findElement(By.name("q")).getAttribute("value"),
                equalTo("dsa"));
    }
}