With such naming convention we can write real specification and include details about specified behaviour in method name, what is very convenient when reading test reports and analyzing errors.
Test method (also called feature method) is logically divided into few blocks, each with its own purpose. Blocks are defined like labels in Java (but they are transformed with Groovy AST transform features) and some of them must be put in code in specific order.
Most basic and common schema for Spock test is:
In next section I am going to describe each block shortly with little examples.
When block contains action we want to test (Spock documentation calls it 'stimulus'). This block always occurs in pair with
then block, where we are verifying response for satisfying certain conditions. Assume we have this simple test case:
class UserSpec extends Specification {
// ...
def "should assign user to comment when adding comment to user"() {
given:
User user = new User()
Comment comment = new Comment()
when:
user.addComment(comment)
then:
comment.getUserWhoCreatedComment().equals(user)
}
// ...
}
In
when block there is a call of tested method and nothing more. After we are sure our action was performed, we can check for desired conditions in
then block.
Then block is very well structured and its every line is treated by Spock as boolean statement. That means, Spock expects that we write instructions containing comparisons and expressions returning true or false, so we can create
then block with such statements:
user.getName() == "John"
user.getAge() == 40
!user.isEnabled()
Each of lines will be treated as single assertion and will be evaluated by Spock.
Sometimes we expect that our method throws an exception under given circumstances. We can write test for it with use of
thrown method:
class CommentSpec extends Specification {
def "should throw exception when adding null document to comment"() {
given:
Comment comment = new Comment()
when:
comment.setCommentedDocument(null)
then:
thrown(RuntimeException)
}
}
In this test we want to make sure that passing incorrect parameters is correctly handled by tested method and that method throws an exception in response. In case you want to be certain that method does not throw particular exception, simply use notThrown method.
expect block
Expect block is primarily used when we do not want to separate when and then blocks because it is unnatural. It is especially useful for simple test (and according to TDD rules all test should be simple and short) with only one condition to check, like in this example (it is simple but should show the idea):
def "should create user with given name"() {
given:
User user = UserTestFactory.createUser("john doe")
expect:
user.getName() == "john doe"
}
More blocks!
That were very simple tests with standard Spock test layout and canonical divide into given/when/then parts. But Spock offers more possibilities in writing tests and provides more blocks.
setup/cleanup blocks
These two blocks have the very same functionality as the def setup and def cleanup methods in specification. They allow to perform some actions before test and after test. But unlike these methods (which are shared between all tests) blocks work only in methods they are defined in.
where - easy way to create readable parameterized tests
Very often when we create unit tests there is a need to "feed" them with sample data to test various cases and border values. With Spock this task is very easy and straighforward. To provide test data to feature method, we need to use where block. Let's take a look at little the piece of code:
def "should successfully validate emails with valid syntax"() {
expect:
emailValidator.validate(email) == true
where:
email << [ "test@test.com", "foo@bar.com" ]
}
In this example, Spock creates variable called email which is used when calling method being tested. Internally feature method is called once, but framework iterates over given values and calls expect/when block as many times as there are values (however, if we use @Unroll annotation Spock can create separate run for each of given values, more about it in one of next examples).
Now, lets assume that we want our feature method to test both successful and failure validations. To achieve that goal we can create few parameterized
variables for both input parameter and expected result. Here is a little example:
def "should perform validation of email addresses"() {
expect:
emailValidator.validate(email) == result
where:
email << [ "WTF", "@domain", "foo@bar.com" "a@test"
result << [ false, false, true, false ]
}
Well, it looks nice, but Spock can do much better. It offers tabular format of defining parameters for test what is much more readable and natural. Lets take a look:
def "should perform validation of email addresses"() {
expect:
emailValidator.validate(email) == result
where:
email | result
"WTF" | false
"@domain" | false
"foo@bar.com" | true
"a@test" | false
}
In this code, each column of our "table" is treated as a separate variable and rows are values for subsequent test iterations.
Another useful feature of Spock during parameterizing test is its ability to "unroll" each parameterized test. Feature method from previous example could be defined as (the body stays the same, so I do not repeat it):
@Unroll("should validate email #email")
def "should perform validation of email addresses"() {
// ...
}
With that annotation, Spock generate few methods each with its own name and run them separately. We can use symbols from
where blocks in @Unroll argument by preceding it with
'#' sign what is a signal to Spock to use it in generated method name.
What next?
Well, that was just quick and short journey through Spock and its capabilities. However, with that basic tutorial you are ready to write many unit tests. In one of my future posts I am going to describe more features of Spock focusing especially on its mocking abilities.