Generating values of more complex types
Generators for complex types have many options for generating constituent values.
Using the SourceOfRandomness handed to the generator directly
import java.awt.Polygon;
public class PolygonGenerator extends Generator<Polygon> {
public PolygonGenerator() {
super(Polygon.class);
}
@Override public Polygon generate(
SourceOfRandomness r,
GenerationStatus status) {
int numberOfPoints = Math.abs(r.nextInt());
int xs = new int[numberOfPoints];
for (int i = 0; i < numberOfPoints; ++i)
xs[i] = r.nextInt();
int ys = new int[numberOfPoints];
for (int i = 0; i < numberOfPoints; ++i)
ys[i] = r.nextInt();
return new Polygon(xs, ys, numberOfPoints);
}
}
Calling for a generator for values of a specific type via gen()
Generators that are made available to the ServiceLoader or referenced via @From can access other such generators via the superclass method gen().
- gen().type(...)
This method asks for an arbitrary generator that can produce instances of the given type.
public class Counter {
private int count;
public Counter(int count) {
this.count = count;
}
// ...
}
public class Counters extends Generator<Counter> {
public Counters() {
super(Counter.class);
}
@Override public Counter generate(
SourceOfRandomness random,
GenerationStatus status) {
return new Counter(
Math.abs(gen().type(int.class).generate(random, status)));
}
}
- gen().constructor(...)
This method gives a generator that produces instances of the given type by invoking a constructor reflectively, generating random values for the constructor’s arguments using available generators. This works a lot like annotating a property parameter with @From(Ctor.class). Any configuration annotations on the constructor parameters will be honored.
public class Counter {
private int count;
public Counter(int count) {
this.count = count;
}
// ...
}
public class TrafficTracker {
private final Counter counter;
public TrafficTracker(Counter counter) {
this.counter = counter;
}
}
public class TrafficTrackers extends Generator<TrafficTracker> {
public TrafficTrackers() {
super(TrafficTracker.class);
}
@Override public Counter generate(
SourceOfRandomness random,
GenerationStatus status) {
return new TrafficTracker(
gen().constructor(Counter.class, int.class)
.generate(random, status));
}
}
- gen().fieldsOf(...)
This method gives a generator that produces instances of the given type by instantiating using an accessible zero-arg constructor, and generating random values for the instance’s fields using available generators. This works a lot like annotating a property parameter with @From(Fields.class). Any configuration annotations on the fields will be honored.
public class Counter {
private int count;
// ...
}
public class TrafficTracker {
private final Counter counter;
public TrafficTracker(Counter counter) {
this.counter = counter;
}
}
public class TrafficTrackers extends Generator<TrafficTracker> {
public TrafficTrackers() {
super(TrafficTracker.class);
}
@Override public Counter generate(
SourceOfRandomness random,
GenerationStatus status) {
return new TrafficTracker(
gen().fieldsOf(Counter.class).generate(random, status));
}
}
- gen().parameter(...)
This method gives a generator that can produce instances of the type of the given reflected method parameter, and that honors all of the configuration annotations on the parameter.
- gen().field(Class<?>, String)
This method gives a generator that can produce instances of the type of the field of a given name on the given type, and that honors all of the configuration annotations on the field.
- gen().field(Field)
This method gives a generator that can produce instances of the type of the given reflected field, and that honors all of the configuration annotations on the field.
- gen().make(...)
This method makes an instance of the given generator class, makes the available generators available to it, and configures it with whatever configuration annotations live on the generator class.
public class NonNegativeInts extends Generator<Integer> {
public NonNegativeInts() {
super(Arrays.asList(Integer.class, int.class));
}
@Override public Integer generate(
SourceOfRandomness random,
GenerationStatus status) {
return Math.abs(random.nextInt());
}
}
public class Counter {
private int count;
public Counter(int count) {
this.count = count;
}
// ...
}
public class Counters extends Generator<Counter> {
public Counters() {
super(Counter.class);
}
@Override public Counter generate(
SourceOfRandomness random,
GenerationStatus status) {
return new Counter(
gen().make(NonNegativeInts.class)
.generate(random, status));
}
}
Generators for types with component types: ComponentizedGenerator
Extend class ComponentizedGenerator instead of Generator when the type of values you need to generate has component types; for example, collections and maps. This is usually necessary for generating values for types that involve generics.
public final class Either<L, R> {
private final Optional<L> left;
private final Optional<R> right;
private Either(Optional<L> left, Optional<R> right) {
this.left = left;
this.right = right;
}
public static <A, B> Either<A, B> makeLeft(A left) {
return new Either<>(Optional.of(left), Optional.empty());
}
public static <A, B> Either<A, B> makeRight(B right) {
return new Either<>(Optional.empty(), Optional.of(right));
}
public <T> T map(
Function<? super L, ? extends T> ifLeft,
Function<? super R, ? extends T> ifRight) {
return left.map(ifLeft).orElseGet(() -> right.map(ifRight).get());
}
@Override public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Either<?, ?>))
return false;
Either<?, ?> other = (Either<?, ?>) o;
return left.equals(other.left) && right.equals(other.right);
}
@Override public int hashCode() {
return Objects.hash(left, right);
}
@Override public String toString() {
return map(
left -> "Left[" + left + ']',
right -> "Right[" + right + ']');
}
}
public class EitherGenerator extends ComponentizedGenerator<Either> {
public EitherGenerator() {
super(Either.class);
}
@Override public Either<?, ?> generate(
SourceOfRandomness random,
GenerationStatus status) {
return random.nextBoolean()
? Either.createLeft(componentGenerators().get(0).generate(random, status))
: Either.createRight(componentGenerators().get(1).generate(random, status));
}
@Override public int numberOfNeededComponents() {
return 2;
}
}
@RunWith(JUnitQuickcheck.class)
public class Eithers {
@Property public void constrained(
Either<
@InRange(minInt = 0) Integer,
@InRange(minDouble = -7.0, maxDouble = -4.0) Double> e) {
e.map(
left -> {
assertThat(left, greaterThanOrEqualTo(0));
return 0;
},
right -> {
assertThat(
right,
allOf(greaterThanOrEqualTo(-7.0), lessThanOrEqualTo(-4.0)));
return 1;
}
);
}
}