Do yourself a favour and don’t test using HTTPS
One place I see Selenium users stubbing their toes on time and again is around automating HTTPS connections. I’m about to tell you that you should save yourself a lot of pain and just not do it.
Having a secure connection in production is an extremely good idea. Especially at places like checkout and authorization. But in testing? Not so much.
There is exactly one situation where you need to be running HTTPS in testing, and that is if you are using certificates as an authentication means. For every other test scenario, in test, you can run things just as HTTP. Not only can you watch the network traffic in the clear over HTTP but you don’t have to worry about the trust issues certificates introduce.
And there is almost always trust issues.
Why?
Because ‘real’ certificates cost money. The whole notion of security is based around trust, and the way to establish that trust is through money and verification. If you look in your browser, it will list somewhere all the CA (Certificate Authority) root certificates that it trusts by default. Those vendors pay non-trivial amounts of money to get in there. And then they charge non-trivial amounts of money end consumers to sign a certificate with their root certificate. Production sites will (almost) always go that route since your customers are likely to be a little concerned about all the browser warnings about things being wrong with the certificate.
In test though, machines are often rebuild and used for multiple purposes so companies are loath to spend the money on real certificates. When manual testing, this isn’t anything more than a nuisance dialog to dismiss, but when automating, it is much more annoying.
The problem is that the error box is not part of the application, but is part of the browser. In Selenium 1.x there are some workarounds, and I believe Selenium 2.x and WATiR solve this by low-level control of the browser.
The easier solution though, is to just not use HTTPS in the testing environment. Sure, your testing machines won’t be as ‘production-like’ as they might otherwise be, but you have to ask yourself, does that materially affect the quality of your testing?. In most situations, it won’t. In fact, I would argue that it increases the breadth of testing available to you; both manually and in an automated fashion.
edit: To be clear, the workaround mentioned are just some of the possible solutions in Selenium 1.x for dealing with HTTPS pages. There are a lot of situations where it will Just Work. Especially in RC where the server is a proxy and certificates get injected on the fly. I would still say in those cases to turn off HTTPS though; it is really hard to figure out what is going on at a network level when it is encrypted.