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This page describes the different strategies and expectations related to the testing of DDF.


The content of this page is still being worked.


End to End Tests

End to end tests refer to tests that exercise the entirety of a DDF distribution, with a focus on the standard DDF configurations that would be used in operational environments. The goal of those tests is to guarantee that a properly installed and configured distribution of DDF will work as expected. End to end tests run in a container (Karaf) installed and configured the same way a customer would use the distribution. Real dependencies such as LDAP, IDP, SolrCloud, etc., should be used. End-to-end tests can vary from gray-box tests using a tool like PaxExam, to black-box tests using tools like Citrus or SoapUI.

As of today, DDF end-to-end tests are written using Pax Exam and can be found here.

Component Tests

Component tests (a.k.a. Service tests) focus on a specific DDF component or service. Their basic goals are to:


For simple components that only have one or two classes (e.g., plugins), component tests may be used as a substitute to unit tests.

Unit Tests

Unit tests usually focus on a single class. The goal of a unit test is to ensure that the class under test respects its contract and behaves as expected under all possible scenarios, including invalid inputs, dependency failures, exception, etc. Unit tests use a simple runner such as JUnit or Spock and mock or stub their dependencies using Mockito or Spock to test all possible failures scenarios.

Like component tests, a class' external dependencies are usually mocked out so that downstream failures can be properly tested. There are however cases when using a real dependency is acceptable. However, that approach should be the exception rather than the rule and should not cause the tests to take longer to run and go against any of the Unit Testing BestPractices.

Test Types Comparison





White box

Gray box

Black box


Single class

Multiple classes making up a service or components; usually contained in a single maven module

Application as a whole


All methods, input/output combinations, conditionals, exceptions, etc.; aim for 100%

Service or component external interfaces, including input/output and errors combinations

Application installation, configurations and deployments; interactions with other applications and external systems


All external classes

External components and services, but usually not embedded libraries

External systems not part of the code base

Time to run


Few minutes

Minutes to hours


Every build; when class changed

Every build; when component/service or one of its dependencies changed

Nightly to a few times a day - unless there's a way to know what tests to run based on the changes made


The overall strategy is to achieve a better balance between end to end, component and unit tests. Over time, the distribution of tests should shift towards the test pyramid, with 70% unit tests, 20% component tests and 10% end to end tests.


  • Even though unit tests are usually easier to write, faster to run, provide better coverage, and make it easier to isolate a problem, they are also the most brittle and the most likely to change as they are closely tied to the component's design and class structure. Applying good object-oriented practices can help mitigate this issue (see Object-Oriented Programming References).
  • Even though component and service tests are a great way to get quick coverage on a bigger area of the code, it is important to keep their goal in mind, i.e., validating the external contract the component has with other components, as well as ensuring it respects other components' external contract when calling out to them. Their goal is not to achieve high internal code coverage.
  • End to end tests are the most difficult to implement and the slowest to run and as such should be kept to a minimum. If a test can be added to the end to end suite or the component suite, it should be added to the latter.

New Components and Services

For new components and services, the pyramid strategy should be followed. Unit tests form the base and account for the greatest amount of testing.  The proper component tests are added to validate APIs and interactions with other components and services. Finally, any new end to end tests added to verify that the component is functional inside the distribution.

Existing Components and Services

For existing components and services, a different strategy may be needed.



Existing coupling between components and feature files can make writing good component tests difficult, if not impossible. Cleaning up feature files and component dependencies should only be considered if the impact is well understood and does not introduce too much risk. Otherwise, component testing should be postponed until those issues have been properly addressed.



Object-Oriented Programming