Why do we use WebDriver instead of Selenium IDE?

Why not just record in the IDE and play the recording with WebDriver???

The IDE Does Not Know What to Wait For

Suppose Bob is performing manual checks and recording his interaction with Selenium IDE. He performs an operation that takes a while to update the GUI, and when the operation has finished, he clicks a button. Bob knows that the GUI has finished updating because a spinner that was show when the operation started is removed when the operation is finished. How is the IDE going to capture the fact that the operation must have finished before clicking on the button? (Note here this is not a case where the button is disabled until the operation is finished.) This is not a hypothetical: when you test dynamic tables (like those managed by DataTables), the user can change anything at any time.

This can be one of the reasons a sequence of commands created with the IDE would fail with WebDriver. It just does not know what to wait for.

It is possible to add waits manually in the IDE but if you are doing this, then you are no longer "just record[ing] all of our test cases". And what you are doing becomes more like writing code for WebDriver.

Users are Inefficient

Not long ago there was a Selenium question in which the user wanted to get Selenium to click on the last record in a table that had multiple pages of records. So the question was, how can I page through the table, all the way down to the last page and then click the last record? Someone (maybe me, maybe someone else) pointed out that if the table is sortable, it could be sorted in reverse order and then the Selenium code could click on the first record. That's 2 operations rather than p+1 operations: clicking p times, where p is the number of pages, plus 1 time for the click on the record.

When we write code for WebDriver, we have the opportunity to write the tests to avoid taking the scenic route to get the results we want. See the next point for the technical details as to why it matters.

Selenium Operations Can Be Costly

If the software that runs your Selenium commands is local, and your browser is local, you may not feel that Selenium operations can be costly but if you run your commands on one machine and the browser is remote, then you will notice a significant slowdown. For instance, if you spawn your browser in a Sauce Labs VM or in a BrowserStack VM to run a test suite, network delays are going to add significant time to how long it takes the suite to complete. For a complete application test suite, this can mean many minutes more.

The IDE produces a sequence of commands that each require a round-trip between the Selenium script and the browser. Each round-trip adds up. Suppose I want to check that two elements contain the same text. I'm not going to use Selenese because I don't usually use the IDE but using WebDriver code in Python, the script could be:

a = driver.find_element_by_id("a")
b = driver.find_element_by_id("b")
assert_equal(a.text, b.text)

This code requires 4 round-trips: one round-trip per find_element... and one per access to the text field. The same test could be written:

a_text, b_text = driver.execute_script("""
var a = document.getElementById("a");
var b = document.getElementById("b");
return [a.textcontent, b.textContent];
""");
assert_equal(a_text, b_text);

This needs only one round-trip. When you use the IDE to record actions, the sequence of commands is like the earlier snippet: lots of round-trips. When you write your code for WebDriver, you have the opportunity to optimize as you code.

This does not mean that the Selenium IDE has no use but I would never ever think of just recording tests with it and then playing those recordings with WebDriver.

If you are a newbie, you can actually use 80% of your IDE script as your webdriver JAVA script, u just have to slightly improvise your exported IDE script and it will work fine.

But when you start testing complex functionalities you have to learn some of the basic java methods to work it out!

why cant we just record all of our test cases in IDE, export it to java/webdriver and run it in webdriver

Great question, and here is the answer:

Selenium IDE is a Record and Playback tool, which is very easy to use, but it's very unreliable. Record and playback is typically a frowned upon in web applications. Since web applications are frequently changed, the IDE is not an ideal solution for a production environment, because of the maintenance nightmare that may arise.

Let me give you a practical example. You record your test, and you find an element with a dynamic ID. Sure we can import it into eclipse, but what happens when that test starts failing down the road? why not simply make your test agile and independent to catch these in the first place.

It also boils down to your principles of test automation. Test automation in MY opinion (and several other professionals), believe that test automation should be approached from a programming perspective. Programmers should write the tests, and maintain the tests. Ideally, your quality assurance personnel should be trained to write and maintain their own tests.

So again, back to your question, the IDE is designed to be a quick solution to automation, NOT a solution to a full regression suite.

And can anyone please explain why IDE recorded scripts fail in Webdriver?

I haven't used the IDE in a while, but the reason they fail, is because the scripts that are exported, are simply the steps, not an entire java file. This also is because Selenium IDE exportations are supposed to be agnostic when it comes to how to run your test. Say I'm a user of jUnit.. what if Selenium IDE exported it to TestNG all the time? That wouldn't be fair.. honestly i'd rather create my own tests than changing that one line every single time i create my test file.

You may read the full text of a research conducted, called Why do Record/Replay Tests of Web Applications Break?

Why can't we just record all of our test cases in Selenium IDE, export it to Java/WebDriver and run it in WebDriver with Eclipse.

You can actually do this with Selenium IDE quite easily. Record your test case / test suite in Selenium IDE, export to "Java / JUnit 4 / Webdriver" to a .java file. This will generate a JUnit test that you can import and run from Eclipse (with the correct version of JUnit of course).

It's not 100% reliable, and you may need to make some manual changes/corrections, but in general it works pretty well. Start with a single small testcase and work from there.