hegel library

Property-based testing for Dart, powered by the Hegel engine.

A property is a claim about every input, checked against inputs the engine generates. When one fails, the engine shrinks the failing case to the smallest one that still fails and remembers it, so the property keeps failing until the bug is fixed.

Classes

Database
Where discovered counterexamples are persisted.
DeferredGenerator<T>
The generator deferred returns, before and after it is defined.
Generator<T>
A recipe for values of type T.
Invariant
Something that must be true between steps.
Pool<T>
A set of values a stateful test made, that the engine can choose among.
Rule
One thing a stateful test can do.
Settings
Configuration for one run.
StateMachine
A system under test, its model, and the steps between them.
TestCase
One test case, as a property body sees it.
TextGenerator
Generates strings over an alphabet.

Enums

Backend
Where the engine's randomness comes from.
HealthCheck
A health check the engine may abort a run over.
Mode
Whether to run the full loop or a single test case.
Phase
One phase of the property-test loop.
Verbosity
How much the engine says while it runs.

Constants

everyHealthCheck → const Set<HealthCheck>
Every health check, for turning the lot off.
everyPhase → const Set<Phase>
Every phase, which is also what the engine does by default.

Functions

bigIntegers({BigInt? min, BigInt? max}) → Generator<BigInt>
Generates integers of any width between min and max inclusive.
booleans({double probability = 0.5}) → Generator<bool>
Generates true with probability probability, false otherwise.
bytes({int minLength = 0, int? maxLength}) → Generator<Uint8List>
Generates byte strings of minLength to maxLength bytes.
characters({String? codec, int? minCodepoint, int? maxCodepoint, List<String>? categories, List<String>? excludeCategories, String? includeCharacters, String? excludeCharacters}) → TextGenerator
Generates single characters, drawn the way text draws them.
composite<T>(T build(TestCase testCase)) → Generator<T>
Generates values build puts together out of draws of its own.
dates({DateTime? min, DateTime? max}) → Generator<DateTime>
Generates dates between min and max inclusive.
dateTimes({DateTime? min, DateTime? max}) → Generator<DateTime>
Generates dates and times between min and max inclusive.
deferred<T>() → DeferredGenerator<T>
A generator that stands in for one not written yet.
domains({int maxLength = 255}) → Generator<String>
Generates fully-qualified domain names of at most maxLength characters.
doubles({double min = double.negativeInfinity, double max = double.infinity, bool? allowNan, bool? allowInfinity, bool excludeMin = false, bool excludeMax = false}) → Generator<double>
Generates doubles between min and max.
durations({Duration? min, Duration? max}) → Generator<Duration>
Generates durations between min and max inclusive.
emails() → Generator<String>
Generates email addresses, per RFC 5321 and 5322.
fromRegex(String pattern, {bool fullMatch = true, TextGenerator? alphabet}) → Generator<String>
Generates strings matching pattern, in Python re syntax.
integers({int? min, int? max}) → Generator<int>
Generates integers between min and max inclusive.
ipAddresses({InternetAddressType? type}) → Generator<InternetAddress>
Generates IP addresses of type, or of either kind when none is given.
just<T>(T value) → Generator<T>
Generates value and nothing else.
lists<T>(Generator<T> elements, {int minLength = 0, int? maxLength, bool unique = false}) → Generator<List<T>>
Generates lists of what elements generates.
maps<K, V>(Generator<K> keys, Generator<V> values, {int minLength = 0, int? maxLength}) → Generator<Map<K, V>>
Generates maps of what keys and values generate.
oneOf<T>(List<Generator<T>> options, {List<int>? weights}) → Generator<T>
Generates values from whichever of options each case picks.
optional<T>(Generator<T> value) → Generator<T?>
Generates values from value, or null.
property(Object? description, FutureOr<void> body(TestCase), {Settings settings = const Settings(), String? reproduce, bool? printBlob, String? testOn, Timeout? timeout, Object? skip, Object? tags, Map<String, dynamic>? onPlatform, int? retry}) → void
Registers a property as a package:test test.
runProperty(FutureOr<void> body(TestCase), {Settings settings = const Settings(), String? databaseKey, String? reproduce, bool? printBlob, void onDiagnostic(String line)?}) → Future<void>
Checks body against test cases the engine chooses.
runStateful(TestCase testCase, StateMachine machine, {int minConcurrency = 1, int maxConcurrency = 1}) → Future<void>
Runs machine against test cases the engine sequences.
sampledFrom<T>(List<T> values) → Generator<T>
Generates values picked from values.
sets<T>(Generator<T> elements, {int minLength = 0, int? maxLength}) → Generator<Set<T>>
Generates sets of what elements generates.
text({int minLength = 0, int? maxLength, String? codec, int? minCodepoint, int? maxCodepoint, List<String>? categories, List<String>? excludeCategories, String? includeCharacters, String? excludeCharacters}) → TextGenerator
Generates strings of minLength to maxLength characters.
times({Duration? min, Duration? max}) → Generator<Duration>
Generates times of day between min and max inclusive.
tuple2<A, B>(Generator<A> first, Generator<B> second) → Generator<(A, B)>
Generates pairs of what first and second generate.
tuple3<A, B, C>(Generator<A> first, Generator<B> second, Generator<C> third) → Generator<(A, B, C)>
Generates triples of what first, second and third generate.
tuple4<A, B, C, D>(Generator<A> first, Generator<B> second, Generator<C> third, Generator<D> fourth) → Generator<(A, B, C, D)>
Generates quadruples of what first to fourth generate.
urls() → Generator<String>
Generates http and https URLs, per RFC 3986.
uuids({int? version}) → Generator<String>
Generates UUIDs in the canonical 8-4-4-4-12 form.

Exceptions / Errors

AssumptionFailed
Signals that an assumption did not hold, so this test case is invalid.
PropertyError
Raised when a run reached no verdict about the property.