AssertJ is an alternative matching library to the widely used Hamcrest matchers. For my own projects I in fact have changed to solely use AssertJ — I just find the fluid interfaces and extensibility quite appealing.
You can write custom assertions as follows:
Imagine a coffee with a strength and a drink type, such as Espresso or Latte. A custom CoffeeAssert validates coffee instances based on their custom business logic — in this case their properties.
public class CoffeeAssert extends AbstractAssert<CoffeeAssert, Coffee> {
public CoffeeAssert(Coffee actual) {
super(actual, CoffeeAssert.class);
}
public static CoffeeAssert assertThat(Coffee actual) {
return new CoffeeAssert(actual);
}
public CoffeeAssert hasType(Coffee.Type type) {
isNotNull();
if (actual.getType() != type) {
failWithMessage("Expected the coffee type to be <%s> but was <%s>", type, actual.getType());
}
return this;
}
// hasStrength(Strength) omitted ...
public CoffeeAssert isNotDecaf() {
isNotNull();
if (actual.getStrength() == Coffee.Strength.DECAF) {
failWithMessage("Expected a coffee but got decaf!");
}
return this;
}
}Coffee instances can then simply be validated using the custom assertion. The static import of the assertThat has to refer to CoffeeAssert.
import static com.example.coffee.CoffeeAssert.assertThat;
...
Coffee coffee = new Coffee();
coffee.setStrength(Strength.STRONG);
coffee.setType(Type.ESPRESSO);
assertThat(coffee)
.hasType(Type.ESPRESSO)
.isNotDecaf();The use of custom assertions can vastly improve the quality of your test code.
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| Published on Java Code Geeks with permission by Sebastian Daschner, partner at our JCG program. See the original article here: Write custom AssertJ assertions Opinions expressed by Java Code Geeks contributors are their own. |
