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This guide will explain why you should write automatic tests for your web application. By referring to this guide, you will be able to:

1 Testing Software

There are two ways to test software: have an actual person use the software or have a program automatically test the software.

People who test software "by hand" often do this under the heading "Quality Assurance" or "QA". See jobs in Salzburg or jobs in Berlin.

But even if you have a QA department for your project, as a developer you still will write automated tests too.

1.1 Why write automatic tests?

There are many reasons why you would want to write tests for your program:

  • when you first write the program: to know if the program works (as specified)
  • to know if it still works after adding a new feature
  • to know if it still works after refactoring the code
  • to know if it still works after updating the dependencies

1.2 Example test

This simple example in Javascript tests a function foo:

describe('foo function', function() {

  it('converts number 1 correctly', function() {
    let input = { value: 1, language: english };
    assert.equal(foo(input), 'one');


The test framework gives you the possibility to group your tests. In this example this is done with describe and it.

This test of the function foo consists of:

  • a setup phase, where we prepare a data strucure we need later
  • the calling of the function foo with the prepared input
  • comparing the output of foo to the expected output

For the last step the word assert or assertion is often used.

Here is a longer example in ruby:

    describe Customer do

      before do
        @movie_1 ="Iron Man 3", Movie::NEW_RELEASE)
        @movie_2 ="Avatar",     Movie::REGULAR)
        @movie_3 ="Brave",      Movie::CHILDRENS)
        @customer ="Vroni")

      describe "customer statement" do
        it "is printed correctly for a new release movie" do
          # [...]
        it "is summed up correctly for 3 movies" do
          @customer.add_rental(, 2))
          @customer.add_rental(, 3))
          @customer.add_rental(, 4))
          @customer.statement.must_match /Amount owed is 12.5/
          @customer.statement.must_match /You earned 4 frequent renter points/

Here the setup phase has been extracted to a before block. This is run before every test inside the same describe block. The means that the variable will be reset before each test, if you change @movie_1 in the first test this will not affect the second test.

In this example a more complex assertion is used: must_match will do a pattern match on the resulting string.

1.3 Types of Tests

As a beginner you should distinguish at least two types of tests:

  • unit test - tests one specific unit of code (be it a class, a package, one model, one view....)
  • integration test - tests the whole program from the perspective of a user

Integration tests give you more valuable insights from a users perspective, e.g.: "the shopping cart checkout does not work". Unit tests help developers find the part of the program that is responsible for a problem: "the cookie store class breaks if you store an undefined value".