Often, when test automation people come over to ruby, they bring constructs from their previous language – “you can write fortran in any language” – missing out on the expressiveness that ruby can give you. A great example of this is in array manipulation. Some common scenarios:
- you need to iterate over each element (eg: clicking each radio button on a page)
- you need to select elements that match certain criteria (eg: getting the text value for every other row in a table)
- you need to reject elements that match certain criteria (eg: if there is a disabled text field, ignore it)
- you need to transform each element in a particular way (eg: you need to convert a list of names to upper case)
Ruby provides expressive and pretty ways of doing the above. What we’re going to do next is look at the sort of code that ruby-n00bs often write to deal with the above, then contrast it with ‘the ruby way’ of doing the same thing. Hopefully, you’ll agree that the ruby way is considerably cleaner, more expressive and cuts out lots of needless boilerplate code. So…
Iterating over each element in an array
In the old school world, the normal way to iterate over an array is to use a for loop. To figure out how many times to iterate you’d get the length of the array. The for loop gives you an index, which you’d then use to access the next element in the array. Here’s an example in ruby that prints off each element of an array:
a = [1, 2, 3, 4, 5]
for i in 0..(a.size - 1)
puts a[i]
end
Not very expressive, is it. Now for the ruby equivalent:
a = [1, 2, 3, 4, 5]
a.each {|number| puts number}
Now, it’s fairly uncommon to see the above mistake, even in ruby-n00b code. Learning the ‘each’ method seems to be a rite-of-passage that almost everyone goes through.
Transforming each element of an array
So, as we mentioned, very few ruby programmers don’t know about or don’t use ‘each’. Annoyingly, it is often incorrectly used by n00bs to transform each element of an array. The following is an example where an array of lower case words is transformed into an array of upper case words:
lower_case = ["hi", "these", "are", "some", "words"]
upper_case = []
lower_case.each do |word|
upper_case << word.upcase
end
puts upper_case.inspect
#=> ["HI", "THESE", "ARE", "SOME", "WORDS"]
Every element of the array is looped through (correct), the transformation is done (‘word.upcase’ – correct); the mistake comes when adding that element to a new array. Ruby has a method that does all this for you; it’s called ‘collect’.
lower_case = ["hi", "these", "are", "some", "words"]
upper_case = lower_case.collect { |word| word.upcase }
puts upper_case.inspect
#=> ["HI", "THESE", "ARE", "SOME", "WORDS"]
What collect does is iterate over the array, ‘collect’ the result of the block (in this case the changing to uppercase of the block argument), store the result in a new array. It’s much shorter, but the main thing is that it’s more expressive. Here’s an example of where you could use it. Say you had a class that represented a page that you’re testing, and say that it contains a method that returns the text of every link on the page. Here’s the old school way:
class MyPage
def links_text
text_array = []
@browser.links(:xpath, "//a").each do |link|
text_array << link.text
end
text_array
end
end
If you change it to use ‘collect’ instead of ‘each’, you’ll have the following instead:
class MyPage
def links_text
@browser.links(:xpath, "//a").collect {|link| link.text}
end
end
Much nicer! Note that you can use ‘map’ instead of ‘collect’ if you like – one is an alias for the other.
Selecting only elements that meet some criteria
Another case of ‘each’ misuse. . . It’s a common scenario to want to select only certain items from an array – specifically elements that meet certain criteria. An example: given an array containing the numbers 1 to 10, I want to get all the even numbers. Well, one way to describe that criteria is:
element % 2 == 0
If, when the element is divided by 2, there is no remainder; element is an even number. So now, lets look at a ruby-n00b way of getting those elements:
all_numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers = []
all_numbers.each do |number|
even_numbers << number if number%2 == 0
end
#=> [2, 4, 6, 8, 10]
What’s happening? We’re looping through ‘each’ element, and performing our check. ‘If’ the element meet the criteria, add it to an array called ‘even_numbers’. It works, but it’s long winded, and not very expressive. Here’s the ruby way:
all_numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers = all_numbers.select {|number| number%2 == 0}
#=> [2, 4, 6, 8, 10]
Much better. No need to create a new array before performing the check, no boilerplate add-the-element-to-the-new-array code, no dirty ‘if’s; just nice expressive code.
An example of when you’d want to use it? Say you have a table with a bunch of rows and you want a method to return only the rows that have a certain background color. Here’s n00b-style code:
class MyPage
def blue_rows
my_blue_rows = []
@browser.row(:xpath, "//tr").each do |row|
my_blue_rows << row if row.attribute("bgcolor") == "blue"
end
my_blue_rows
end
end
Again, lots of fluff, hard to tell at first glance what’s going on. Here’s the same thing but this time using the ‘select’ method:
class MyPage
def blue_rows
@browser.row(:xpath, "//tr").select {|row| row.attribute("bgcolor") == "blue"}
end
end
Much nicer. Expressive code. No guff.
Rejecting elements that meet certain criteria
Sometimes you want all the elements in an array apart from those which meet certain criteria. It’s almost identical to ‘select’, just. . . the opposite! Instead of selecting items which meet the supplied criteria, ‘reject’ will reject items which meet the criteria. This time, instead of selecting even numbers, we want to reject them, thus getting an array of odd numbers (a bit contrived, I know; we could just select the elements where element%2==1, but this is a tutorial).
all_numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
odd_numbers = []
all_numbers.each do |number|
odd_numbers << number unless number%2 == 0
end
#=> [1, 3, 5, 7, 9]
This time, we don’t add the number ‘if’ it meets the criterial; instead we add it ‘unless’ it meets the criteria. Again, it’s horrible code. The ruby way:
all_numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
odd_numbers = all_numbers.reject {|number| number%2 == 0}
#=> [1, 3, 5, 7, 9]
So when would you want to use it? With a similar example to what we have above, this time we want all the rows that haven’t got a red background. Old school code:
class MyPage
def non_red_rows
my_non_red_rows = []
@browser.row(:xpath, "//tr").each do |row|
my_non_red_rows << row unless row.attribute("bgcolor") == "red"
end
my_non_red_rows
end
end
Long winded, ugly, hard to see what’s going on. Now, we’ll change it to use ruby’s ‘reject’ method:
class MyPage
def non_red_rows
@browser.row(:xpath, "//tr").reject {|row| row.attribute("bgcolor") == "red"}
end
end
Hard to argue against, right? It’s short, expressive and to the point.
Summary: ruby provides nice methods for array manipulation. ‘Each’, ‘select’ and ‘reject’ are only a few of those methods, but they’re the most frequently used (or should be!). I hope this helps make your code shorter, more expressive and easier to maintain.
