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Figuring out how to automate away the pain of routine front-end web testing; the story behind

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Production Bug #001 Fixed

Following yesterday’s private alpha release, I was trying to figure out why some HTML validation tests were failing.

In some cases I was seeing not a JSON response from the validator but an HTML response. This was odd; we ask the HTML validator to return JSON so that it can be parsed more easily (where ‘more easily’ means ‘at all, really’).

Asking the W3C HTML validator to give you a JSON response, it turns out, only has an effect on HTML validation tests that actually work. Pass the validator nonsense values it can’t understand and you don’t get back the JSON you asked for. That’s fair.

Something we were passing to the HTML validator when trying to validate a web page was being interpreted as nonsense.

When validating, we pass the validator the HTML content to validate and tell it the character encoding that the HTML content uses. One of these was confusing the validator.

It’s pretty hard to confuse the HTML validator with invalid HTML, being able to spot that is a lot of what it does for a living. So I looked at the character encoding.

We have to figure out the character encoding after retrieving a web page so that we can pass this useful detail along to the validator. our web page model library does this for us.

For some web pages, we were asking the web page model for the character encoding it reckons was being used. In response it was saying null. That’s computer speak for “I have no idea whatsoever.”

Odd. I paid attention to how one can choose to specify the character encoding of a web page when making the web page model. There are three ways. I won’t go in to them here. But three ways there are and three ways I had covered.

What I hadn’t considered were cases where the character encoding for a web page could not be determined. Some times the character encoding is not specified at all. Some times it is specified incorrectly, which really means it is not specified at all.

So what happens if you pass a null value to the W3C HTML validator as the character encoding? The validator returns an HTML page stating the that the character encoding you provided isn’t recognised.

A small change sorted this out: if the character encoding for a web page cannot be determined, we tell the HTML validator nothing about the character encoding. It’s happy with this.

Production bug #001 fixed.