Prop<T> final

final class Prop<T>

A property-based test that pairs a Gen with a TestBody.

On failure the framework automatically shrinks the counter-example to a minimal value before reporting it. Use run to register the property as a package:test test case, or check to execute the property directly and inspect the result.

Constructors

Prop()

Prop(String description, Gen<T> gen, FutureOr<void> Function(T) testBody)

Creates a Prop with the given description, gen, and testBody.

Implementation

Prop(this.description, this.gen, this.testBody);

Properties

description final

final String description

Human-readable description used as the test name.

Implementation

final String description;

gen final

final Gen<T> gen

Generator used to produce random samples.

Implementation

final Gen<T> gen;

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

testBody final

final FutureOr<void> Function(T) testBody

The predicate under test.

Implementation

final TestBody<T> testBody;

Methods

check()

Future<Option<PropFailure<T>>> check({int? numTests, int? seed})

Runs the property check and returns the shrunken failure, if any.

Draws up to numTests (default 100) samples from gen. Returns None when every sample passes, or a Some wrapping the minimised PropFailure when a counter-example is found.

Implementation

Future<Option<PropFailure<T>>> check({int? numTests, int? seed}) async {
  final seedNN = seed ?? DateTime.now().millisecondsSinceEpoch;

  var count = 0;
  Option<PropFailure<T>> firstFailure = none();

  final iterator = gen.stream(StatefulRandom(seedNN)).take(numTests ?? 100).iterator;

  while (iterator.hasNext) {
    final value = iterator.next();
    count++;

    final result = await _runProp(value, testBody);

    if (result.isDefined) {
      firstFailure = result.map((f) => f.copy(count: count));
      break;
    }
  }

  return firstFailure.fold(
    () => Future.value(firstFailure),
    (a) => _shrink(a, testBody),
  );
}

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

run()

void run({
  int? numTests,
  int? seed,
  String? testOn,
  Timeout? timeout,
  dynamic skip,
  dynamic tags,
  Map<String, dynamic>? onPlatform,
  int? retry,
})

Registers this property as a package:test test case.

numTests controls how many random samples are drawn (default 100). seed pins the random source so failures are reproducible; when omitted the value is read from the RIBS_CHECK_SEED environment variable, then falls back to the current wall-clock time.

All remaining parameters are forwarded verbatim to package:test's test().

Implementation

void run({
  int? numTests,
  int? seed,
  String? testOn,
  Timeout? timeout,
  dynamic skip,
  dynamic tags,
  Map<String, dynamic>? onPlatform,
  int? retry,
}) {
  test(
    description,
    () async {
      final envSeed = _kIsWeb ? null : Platform.environment['RIBS_CHECK_SEED'];
      final seedNN = seed ?? int.tryParse(envSeed ?? '') ?? DateTime.now().millisecondsSinceEpoch;

      final shrunkenFailure = await check(numTests: numTests, seed: seedNN);

      shrunkenFailure.foreach((a) {
        throw TestFailure(
          '${a.underlying.message}\n'
          'Failed after ${a.count} iterations using value <${a.value}> and initial seed of [$seedNN].\n\n'
          'To reproduce this failure, use seed: $seedNN in your forAllN&#47;Prop call, or run:\n'
          'RIBS_CHECK_SEED=$seedNN dart test --plain-name "$description"\n',
        );
      });
    },
    testOn: testOn,
    timeout: timeout,
    skip: skip,
    tags: tags,
    onPlatform: onPlatform,
    retry: retry,
  );
}

toString() inherited

String toString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);