By default, junit-quickcheck verifies a property in “sampling” mode – it generates 100 tuples of random values for the parameter list of a property, and verifies the property against each of the tuples.
To change the number of generated values, use the trials attribute of the @Property annotation.
@RunWith(JUnitQuickcheck.class)
public class Geography {
@Property(trials = 250) public void northernHemisphere(
@From(Coordinates.class) Coordinate c) {
assumeThat(c.latitude(), greaterThan(BigDecimal.ZERO));
assertTrue(c.inNorthernHemisphere());
}
}
public class Coordinate {
private final BigDecimal latitude, longitude;
public Coordinate(BigDecimal latitude, BigDecimal longitude) {
// argument checks here...
this.latitude = latitude;
this.longitude = longitude;
}
public BigDecimal latitude() { return latitude; }
public BigDecimal longitude() { return longitude; }
public boolean inNorthernHemisphere() {
return latitude.compareTo(BigDecimal.ZERO) > 0;
}
}
public class Coordinates extends Generator<Coordinate> {
@Override public Coordinate generate(
SourceOfRandomness random,
GenerationStatus status) {
return new Coordinate(
BigDecimal.valueOf(random.nextDouble(-90, 90))
.setScale(6, RoundingMode.CEILING),
BigDecimal.valueOf(random.nextDouble(-180, 180))
.setScale(6, RoundingMode.CEILING));
}
}
junit-quickcheck can also verify a property in “exhaustive” mode. In “exhaustive” mode, junit-quickcheck generates trials random values for each of the property’s parameters, and verifies the property against each member of the Cartesian product of the sets of random values for each parameter. This behavior mirrors that of the JUnit Theories runner.
For example, a property such as:
@RunWith(JUnitQuickcheck.class)
public class SimpleProperties {
@Property(trials = 3) public void sum(int a, int b) {
// ...
}
}
might run with these parameter lists:
sum(12987133, 456123400)
sum(-283945, 75089314)
sum(9823745, -139845713)
In “exhaustive” mode:
@RunWith(JUnitQuickcheck.class)
public class SimpleProperties {
@Property(trials = 3, mode = EXHAUSTIVE)
public void sum(int a, int b) {
// ...
}
}
this might run with these parameter lists:
sum(-891273491, 573198457)
sum(719283474, 573198457)
sum(-384571913, 573198457)
sum(-891273491, 6928374)
sum(719283474, 6928374)
sum(-384571913, 6928374)
sum(-891273491, -123420835)
sum(719283474, -123420835)
sum(-384571913, -123420835)
@Only and @AlsoThese annotations can influence how junit-quickcheck chooses the set of values from which to draw the value of a property parameter.
In “sampling” mode, there will be Property.trials() values for each parameter.
@Only, then its values are chosen at random from the specified set.@Also, then those values are used, and trials - |Also.value| values are chosen from generators.@Only wins over @Also.In “exhaustive” mode, there will usually be trials values for a parameter. However:
boolean, Boolean, or an enum, there will be 2, 2, or values().length values, comprising the type’s entire domain.@Only, then only those values (numbering |Only.value|) are used.@Also, then those values are used, and trials -|Also.value|` values are chosen from the generators.trials values are chosen by a generator.@Only wins over @Also.product[ |p| | p in parameters ] number of executions of the property, one for each member of the cross-product of values to be used for each parameter.For example:
@RunWith(JUnitQuickcheck.class)
public class OnlyAndAlso {
public enum Response { YES, NO, UNSURE }
@Property(trials = 45)
public void samplingWithOnly(
int arg0,
boolean arg1,
Response arg2,
@Only({"1", "2", "0", "-1"}) int arg3) {
/*
Invoked 45 times.
45 tuples (arg0, arg1, arg2, arg3) generated.
Each value of each tuple chosen at random from its domain.
Domain of arg3 narrowed by @Only.
*/
}
@Property(trials = 77, mode = EXHAUSTIVE)
public void exhaustiveWithOnly(
int arg0,
boolean arg1,
Response arg2,
@Only({"1", "2", "0", "-1"}) int arg3) {
/*
Invoked 77 * 2 * 3 * 4 times --
once for each choice of 77 randomly chosen arg0,
two possible values of arg1, three possible values of arg2,
and four possible values of arg3.
*/
}
@Property(trials = 45)
public void samplingWithAlso(
int arg0,
boolean arg1,
Response arg2,
@Also({"1", "2", "0", "-1"}) int arg3) {
/*
Invoked 45 times.
45 tuples (arg0, arg1, arg2, arg3) generated.
Each value of each tuple chosen at random from its domain,
except arg3 uses 1, 2, 0, -1, and 41 other randomly generated values.
*/
}
@Property(trials = 77, mode = EXHAUSTIVE)
public void exhaustiveWithOnly(
int arg0,
boolean arg1,
Response arg2,
@Also({"1", "2", "0", "-1"}) int arg3) {
/*
Invoked 77 * 2 * 3 * 77 times --
once for each choice of 77 randomly chosen arg0,
two possible values of arg1, three possible values of arg2,
and the four values named in arg3 plus 73 other randomly generated
values.
*/
}
}
Note: You can use @Only on types that do not have a generator.
By default, junit-quickcheck converts the values specified in @Only and @Also markers to values of the property parameter type via the following strategy:
public static method on the property parameter type called valueOf which accepts a single String argument and whose return type is the type itself.public constructor on the property parameter type which accepts a single Stringargument.Supply a custom conversion strategy if you wish via the by attribute of @Only or @Also.
junit-quickcheck reports the random values and seeds used for verifying a property parameter by logging them to a SLF4J logger named junit-quickcheck.value-reporting, at DEBUG level.
Verifying property propertyMethod from com.your.PropertiesClass with these values: com.your.PropertiesClass.propertyMethod:parameterName = [-42], seed = 8007238959251963394
Add an SLF4J binding JAR file to your test class path and logging configuration for your chosen bound library to see these log messages.
Note: Shrunken counterexamples, minimal or otherwise, are not reported to this log.