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Programming language: Haskell
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Happybara helps you test web applications in Haskell by simulating how a real user would interact with your app. It is agnostic about the driver running your tests and comes with WebKit support via the happybara-webkit package.

Diving In

Before we look at the design of Happybara, let's first take a quick look at a minimal example. We're going to use the following packages:

  • happybara
  • happybara-webkit - This contains a Driver implementation for WebKit.
  • happybara-webkit-server - This packages up the webkit_server binary that we need for happybara-webkit (you could also compile it yourself, but using this package should be a bit more turn-key).

Note: Before you install the happybara-webkit-server package, you'll need to install Qt4.8 or greater. If you need help, follow the capybara-webkit guide.

Alright, let's take a look at a simple example:

{-# LANGUAGE OverloadedStrings #-}

import           Happybara
import           Happybara.WebKit
import           Happybara.WebKit.Server

import           Control.Monad.Base

import qualified Data.ByteString.Char8 as BS
import           Data.Text             as T
import           Data.Text.Encoding    as T

import qualified System.IO             as IO

main :: IO ()
main = run $ do
    visit "http://google.com"

    btn <- findOrFail (button "I'm Feeling Lucky" [disabled False])
    SingleValue value <- getValue btn
    puts $ T.concat [ "Button found: ", value ]

    click btn

    url <- currentUrl
    puts $ T.concat [ "New url: ", url ]

    return ()

run :: Happybara Session a -> IO a
run act = do
    serverPath <- webkitServerPath
    withSession serverPath $ \sess ->
        runHappybara sess act

puts :: Text -> Happybara sess ()
puts txt =
    liftBase $ BS.hPutStrLn IO.stdout $ T.encodeUtf8 txt

Let's first look at main. In this minimal example, we:

  • Visit the google home page.
  • Find an enabled button with the text "I'm Feeling Lucky".
  • Print the value of the button.
  • Click the button
  • Print the new url.

This is just scratching the surface; to get a broader sense of the API, you can keep reading this document, or move on to reading the Haddocks.

Let's change our focus to run now. The first thing to notice is that we parameterized our Happybara monad with Happybara.WebKit.Session; this is our way of saying that we wish to use the WebKit Driver. You see, Happybara has a pluggable driver architecture, and Session is just one (of potentially many) Driver instances. You could just as well use a PhantomJS driver, or Selenium driver.

The rest of the run function merely handles starting up the WebKit server.

Now let's move on to the design and interface of Happybara.


As we've already touched on, Happybara Drivers implement the Happybara.Driver.Driver class.


Note: All searches in Happybara are case sensitive. This is because Happybara heavily uses XPath, which doesn't support case insensitivity.

Happybara features a rich DOM querying system. Queries are performed via the Query class and its respective functions. As we saw earlier, button locator predicates is one example of a query, where locator is a string denoting an id, value, etc, and predicates is a list of filters.

Queries can be performed via find, findOrFail, and findAll.


When querying the DOM, it's often convenient to search in an inexact manner (e.g. via substring, rather than strict equality). And yet there are other times when you know exactly what you want to find, and nothing else will do.

Happybara allows you to demand a particular level of exactness via setExactness. There are three different settings:

  • Exact - Find elements that match exactly.
  • PreferExact - First try to find exact matches; if that fails, fall back to inexact matches.
  • Inexact - Find all elements that partially match - e.g. the given string is infix of (but not necessarily equal to) whatever property (id, attribute, etc) is being queried over.

Matching Strategy

When a query is performed for a single value, and multiple matches are found, you need to decide if that should yield the first result, or fail hard with an AmbiguousElementException. Using setSingleMatchStrategy, these are your two options:

  • MatchFirst
  • MatchOne

By having the matching strategy as part of the monadic state, queries compose in a convenient, consistent way. For instance, consider the following:

fillIn (fillableField "User Name" []) "Charles Strahan"

If you've set MatchFirst, the code above will fill in the first matching field; if you set MatchOne, you'll get an exception if more than one field matched.