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 on generators embedding as fields of the generator
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> {
private final Generator<Integer> nonNegatives =
new NonNegativeInts();
public Counters() {
super(Counter.class);
}
@Override public Counter generate(
SourceOfRandomness random,
GenerationStatus status) {
return new Counter(nonNegatives.generate(random, status));
}
}
Asking 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.
Generators for types with component types: ComponentizedGenerator
Extend class ComponentizedGenerator instead of Generator when the type of values you need to generate have 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.createLeft(componentGenerators().get(0).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;
}
);
}
}