CODEWITHSUNDEEP
javaunit-testingbuilder
piyo
piyo

Reputation: 471

Testing builder pattern in Java

We use the builder pattern extensively in our code base, with built objects all having a toBuilder() method. I want to write a unit test that ensures that no fields have been forgotten in the toBuilder() methods, i.e., for any buildable object, I want to a test roughly like this

MyClass obj = getTestObjectWithRandomData();
assertEquals(obj, obj.toBuilder().build());

Now, I can fairly easy write a basic version of getTestObjectWithRandomData() that uses reflection to assign a bunch of values to the fields of any object. However, the snag is that build() often contains tons of validation checks that will throw exceptions if, for example, a certain integer isn't within a sane range. Writing a generalized version of getTestObjectWithRandomData() that conforms all those class-specific validation checks would be impossible.

So, how can I do what I want to do? I'm tempted to segregate the construction and validation code into different methods so that the test doesn't trip on the validation, but then that means that people have to remember to call validate() or whatever on objects after they create them. Not good.

Any other ideas?

Upvotes: 3

Views: 13642

Answers (1)

djkelly99
djkelly99

Reputation: 630

How about using Lombok? Would that be an option for you? It will auto-generate the builder code and you'll never again have to worry about it. https://projectlombok.org/features/Builder

Simply annotate your classes with @Builder

With Lombok

import lombok.Builder;
import lombok.Singular;
import java.util.Set;

@Builder
public class BuilderExample {
  private String name;
  private int age;
  @Singular private Set<String> occupations;
}

Vanilla Java

import java.util.Set;

public class BuilderExample {
  private String name;
  private int age;
  private Set<String> occupations;

  BuilderExample(String name, int age, Set<String> occupations) {
    this.name = name;
    this.age = age;
    this.occupations = occupations;
  }

  public static BuilderExampleBuilder builder() {
    return new BuilderExampleBuilder();
  }

  public static class BuilderExampleBuilder {
    private String name;
    private int age;
    private java.util.ArrayList<String> occupations;

    BuilderExampleBuilder() {
    }

    public BuilderExampleBuilder name(String name) {
      this.name = name;
      return this;
    }

    public BuilderExampleBuilder age(int age) {
      this.age = age;
      return this;
    }

    public BuilderExampleBuilder occupation(String occupation) {
      if (this.occupations == null) {
        this.occupations = new java.util.ArrayList<String>();
      }

      this.occupations.add(occupation);
      return this;
    }

    public BuilderExampleBuilder occupations(Collection<? extends String> occupations) {
      if (this.occupations == null) {
        this.occupations = new java.util.ArrayList<String>();
      }

      this.occupations.addAll(occupations);
      return this;
    }

    public BuilderExampleBuilder clearOccupations() {
      if (this.occupations != null) {
        this.occupations.clear();
      }

      return this;
    }

    public BuilderExample build() {
      // complicated switch statement to produce a compact properly sized immutable set omitted.
      // go to https://projectlombok.org/features/Singular-snippet.html to see it.
      Set<String> occupations = ...;
      return new BuilderExample(name, age, occupations);
    }

    @java.lang.Override
    public String toString() {
      return "BuilderExample.BuilderExampleBuilder(name = " + this.name + ", age = " + this.age + ", occupations = " + this.occupations + ")";
    }
  }
}

Upvotes: 6

Related Questions