As zmorris points driver.getPageSource().contains("input");
is not the proper solution because it searches in all the html, not only the texts on it.
I suggest to check this question: how can I check if some text exist or not in the page?
and the recomended way explained by Slanec:
String bodyText = driver.findElement(By.tagName("body")).getText();
Assert.assertTrue("Text not found!", bodyText.contains(text));