cout("delete all students");
driver.findElement(By.className("t_courses")).click();
waitAndClick(By.className("t_course_view"));
waitForElementPresent(By.id("dataform tr"));
WebElement dataform = driver.findElement(By.id("dataform"));
while (dataform.findElements(By.tagName("tr")).size() > 1) {
System.out.println("Delete a student...");
By by = By.xpath(String.format("//table[@id='dataform']//tr[%d]//a[4]", 2));
waitForElementPresent(by);
clickAndConfirm(by);
waitForElementPresent(By.id("dataform tr"));