To compare string values we can use the isEqualTo(String) method in AssertJ. But if we want to verify that a string contains a certain variable value we can use string templates. This makes the assertion more readable as we can see what value we expect in the string. To use string templates we must the method isEqualTo(String, Object…​). The first argument is the string template and the following arguments will be the actual values that should be used in the template. Actually the String.format(String, Object…​) method is used behind the scenes to format the string template, but we don’t have to clutter our assertions with that call.

With the returns method in AssertJ we can verify an object using a function. This allows us to verify an object in a very flexible way. We can chain multiple returns method calls to verify multiple aspects of our object. The first argument of the returns method is the expected value of the function call. And the second argument is a function that calls a method on the object we want to verify. A simple function call would be a method reference using the class of the object. But we can also write our own function, where the argument of the function is actual object we are writing the assertion for. To verify the function doesn’t return an expected value we can use the method doesNotReturn.
We can also pass the function to the from method, available in the Assertions class. It can make the assertion more readeable as we can now read the code as: we expect the following value from calling this function.

Writing assertions using the nice fluent API of AssertJ is a joy. Besides some of the basic assertions like isEqualTo AssertJ also has specific assertions for specific types. For example if we want write an assertion to check if a String value starts or ends with an expected value we can use the startsWith(String) or endsWith(String) methods. If we don’t care that a character is upper or lower case we can also use startsWithIgnoringCase(String) or endsWithIgnoringCase(String). Each of the methods also has a counterpart method to check the String value doesn’t start or end with an expected value. For example we can use doesNotStartWith(String) to assert a value does not start with the expected value.

AssertJ has many useful methods to write assertions using a fluid API. If we want to test the toString() method implementation of an object we can of course invoke the toString() method inside an assertThat expression and check with the assert method isEqualTo(String) the value. But AssertJ can make that easier so we don’t have to invoke toString() method ourselves. We can use the assert method hasToString(String) on the object we defined in the assertThat expression and specify our expected value as argument to the method. If we want to assert the toString() method doesn’t return an expected value we can use the assert method doesNotHaveToString(String).

GINQ (Groovy-INtegerate Query) is part of Groovy since version 4. With GINQ we can use SQL-like queries to work with in-memory data collections. If we want to sort the data we can use orderby followed by the property of the data we want to sort just like in SQL we can use order by. By default the sort ordering is ascending and null values are put last. We can change the sort ordering by specifying in desc with the orderby clause. Or to make the ascending order explicitly we use the statement in asc. Each of asc and desc also can take an argument to specify how we want null values to be sorted. The default way is to keep null values last in the ordering. If we want to make this explicit we use nullslast as argument to asc or desc. To have null values in the sorted result first we use the argument nullsfirst.

Since Groovy 4 we can use SQL like queries on in-memory collections with GINQ (Groovy-Integrated Query). GINQ provides some built-in aggregate functions like min, max, sum and others. One of these functions is median. With median we can get the value that is in the middle of the sorted list of values we want to calculate the median for. If the list has an uneven number of elements the element in the middle is returned, but if the list has an even number of elements the average of the two numbers in the middle is returned.

In the following example we see the use of the median function with GINQ:

Groovy supports a tuple type. A tuple is an immutable object to store elements of potentially different types. In Groovy there is a separate Tuple class based on how many elements we want to store in the tuple. The range starts at Tuple0 and ends with Tuple16. So we can store a maximum of 16 elements in a Groovy tuple.
Each of the classes has a constructor that takes all elements we want to store. But the Tuple class also has static factory methods to create those classes. We can use the tuple method and based on how many elements we provide to this method we get the corresponding Tuple object.

In a previous blog post we learned how to use DataVariable and DataVariables to test asynchronous code. Spock also provides PollingConditions as a way to test asynchronous code. The PollingConditions class has the methods eventually and within that accept a closure where we can write our assertions on the results of the asynchronous code execution. Spock will try to evaluate conditions in the closure until they are true. By default the eventually method will retry for 1 second with a delay of 0.1 second between each retry. We can change this by setting the properties timeout, delay, initialDelay and factor of the PollingConditions class. For example to define the maximum retry period of 5 seconds and change the delay between retries to 0.5 seconds we create the following instance: new PollingConditions(timeout: 5, initialDelay: 0.5).
Instead of changing the PollingConditions properties for extending the timeout we can also use the method within and specify the timeout in seconds as the first argument. If the conditions can be evaluated correctly before the timeout has expired then the feature method of our specification will also finish earlier. The timeout is only the maximum time we want our feature method to run.

Testing asynchronous code needs some special treatment. With synchronous code we get results from invoking method directly and in our tests or specifications we can easily assert the value. But when we don’t know when the results will be available after calling a method we need to wait for the results. So in our specification we actually block until the results from asynchronous code are available. One of the options Spock provides us to block our testing code and wait for the code to be finished is using the classes DataVariable and DataVariables. When we create a variable of type DataVariable we can set and get one value result. The get method will block until the value is available and we can write assertions on the value as we now know it is available. The set method is used to assign a value to the BlockingVariable, for example we can do this in a callback when the asynchronous method support a callback parameter.

The BlockingVariable can only hold one value, with the other class BlockingVariables we can store multiple values. The class acts like a Map where we create a key with a value for storing the results from asynchronous calls. Each call to get the value for a given key will block until the result is available and ready to assert.

The log function in the dw::Core module allows to log a value or an expression. The function returns the input unchanged. This means we can wrap our code with the log function and the code is still executed as is, but also logged in a system log. As an extra argument we can specify a String value that will be a prefix to the expression value in the logging output. The fact that the input is also returned makes it very easy to add the log function to our DataWeave expressions.

A .mvn directory in the root of our project can contains some useful extras. For example we can set default Maven options or Java VM options when we run a Maven command. We can also define Maven extensions we want to add to the Maven classpath using the file extensions.xml in the .mvn directory. The Maven extension we want to add can be referenced using a groupId, artifactId and version inside an <extension> element. We can define one or more extensions within the parent element extensions. Once we have defined the extension and run Maven the extension is added to classpath of Maven itself.

Since Groovy 4.0.5 we can use a subscript operator that accepts multiple fields on a java.util.Date and java.util.Calendar objects. And Groovy 4.0.6 extended this subscript operator to any java.time.TemporalAccessor instance. Before these Groovy version we could already use the subscript operator, but we could provide only one field we wanted to access. In a previous post we already have seen this. But now we can use multiple fields to get their values with one statement. We simply define the fields we want as arguments to the subscript operator. Under the hood the subscript operator is implemented by a getAt method that is added as an extension to the Date, Calendar and TemporalAccess classes. The return type is java.util.List and we can combine this with the multiple assignment support in Groovy. In other languages it is also called destructurizing. With multiple assignments we can assign the values from a java.util.List directly to variables.