AssertJ: How to build custom and nested assertions

Question

I need to compare one PatientDTO dto object with other one PatientModel model object.

Both classes are quite similar:

class PatientDTO { private String name; private List<AddressDTO> address; // Constructors, getters and setters } class PatientModel { private String id; private String nameElement; private List<AddressModel> addressElement; // Constructors, getters and setters } class AddressDTO { private String city; private String country; private List<String> linesElement; // Constructors, getters and setters } class AddressModel { private String city; private String countryElement; private List<String> linesElement; // Constructors, getters and setters }

Main differences are:

Some fields are not present on DTOs: PatientDTO.id doesn't exist.
Some field names contains suffixes on Model classes: PatientDTO.name <> PatientModel.nameElement.

Other issue I like to solve, is that:

Address related assertion should be shared. I mean, Address-like classes are present on other classes, for exemple, Organization, Practitioner...

I'd like to build an assertion like this:

PatientDTO patientDTO; PatientModel patientModel; assertThat(patientDTO).isEqual(patientModel);

Shortly:

Should I build a custom assertion?
Should I have an assertion for Address an other one for Patient containing previous Address assertion? How could I get this?
What aboud Address assertion for Patient, Organization

What I want to avoid is code like this:

assertThat(patientDTO).anySatisfy(p->{ assertThat(p.getName()).withFailMessage("expected name: "+ p.getAddress().getCity()).isEqualTo(patientModel.getNameElement()); assertThat(p.getAddress().getCity()).withFailMessage("expected city: "+ p.getAddress().getCity()).isEqualTo(patientModel.getCityElement()); assertThat(p.getAddress().getCountry()).withFailMessage("expected country: "+ p.getAddress().getCountry()).isEqualTo(patientModel.getCountryElement()); ... } );

I want to avoid above code since Patient classes are really large. Here I've shorted them for clarity purpouses.

Any ideas?

Stefano Cordio · Accepted Answer · 2021-12-17 10:52:48Z

The field-by-field recursive comparison could help for this purpose:

PatientDTO patientDTO = new PatientDTO(...); PatientModel patientModel = new PatientModel(...); assertThat(patientDTO).usingRecursiveComparison() .isEqualTo(patientModel);

Some fields are not present on DTOs: PatientDTO.id doesn't exist.

There are a few methods that can be used to tune the comparison and ignore fields:

Directly with ignoringFields(String… fieldsToIgnore)
By regexes with ignoringFieldsMatchingRegexes(String… regexes)
By types with ignoringFieldsOfTypes(Class… typesToIgnore)

Some field names contains suffixes on Model classes: PatientDTO.name <> PatientModel.nameElement.

This is currently not supported and was also asked in https://stackoverflow.com/a/70381488/9714611. We plan to raise a feature request about it and I will update the answer once the issue link is ready.

Address related assertion should be shared. I mean, Address-like classes are present on other classes, for exemple, Organization, Practitioner...

If the target is always isEqualTo, probably a custom assertion implementation is not needed as long as the limitation of the recursive comparison about not being able to compare fields with different names is not a show-stopper. These fields would require ad-hoc comparison until a better solution is available.

If the target is to provide assertions in a domain-specific language, like:

assertThat(patientDTO).hasAddress(addressDTO);

then a custom assertion implementation can be added.

Also, there is an assertions generator with plugins for Maven and Gradle that can be used to generate assertions based on the class attributes.

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