checks
Expectations start with checkThat
. This utility returns a Subject
, and expectations can be checked against the subject. Expectations are defined as extension methods, and different expectations will be available for subjects with different value types.
checkThat(someValue).equals(expectedValue); checkThat(someList).deepEquals(expectedList); checkThat(someString).contains('expected pattern');
Multiple expectations can be checked against the same value using cascade syntax. When multiple expectations are checked against a single value, a failure will included descriptions of the expectations that already passed.
checkThat(someString) ..startsWith('a') ..endsWith('z') ..contains('lmno');
Some expectations return a Subject
for another value derived from the original value - for instance reading a field or awaiting the result of a Future.
checkThat(someString).length.equals(expectedLength); (await checkThat(someFuture).completes()).equals(expectedCompletion);
Fields can be extracted from objects for checking further properties with the has
utility.
checkThat(someValue) .has((value) => value.property, 'property') .equals(expectedPropertyValue);
Some expectations take arguments which are themselves expectations to apply to other values. These expectations take Condition
arguments, which check expectations when they are applied to a Subject
. The ConditionSubject
utility acts as both a condition and a subject. Any expectations checked on the value as a subject will be recorded and replayed when it is applied as a condition. The it()
utility returns a ConditionSubject
.
checkThat(someList).any(it()..isGreaterThan(0));
Some complicated checks may be difficult to write with parenthesized awaited expressions, or impossible to write with cascade syntax. There are which
utilities for both use cases which take a Condition
.
checkThat(someString) ..startsWith('a') // A cascade would not be possible on `length` ..length.which(it() ..isGreatherThan(10) ..isLessThan(100)); await checkThat(someFuture) .completes() .which(equals(expectedCompletion));
Expectations are written as extension on Subject
with specific generics. The library package:checks/context.dart
gives access to a context
getter on Subject
which offers capabilities for defining expectations on the subject's value.
The Context
allows checking a expectation with expect
, expectAsync
and expectUnawaited
, or extracting a derived value for performing other checks with nest
and nestAsync
. Failures are reported by returning a Rejection
, or an Extracted.rejection
, extensions should avoid throwing exceptions.
Descriptions of the clause checked by an expectations are passed through a separate callback from the predicate which checks the value. Nesting calls are made with a label directly. When there are no failures the clause callbacks are not called. When a Condition
is described, the clause callbacks are called, but the predicate callbacks are not called. Conditions can be checked against values without throwing an exception using softCheck
or softCheckAsync
.
extension CustomChecks on Subject<CustomType> { void someExpectation() { context.expect(() => ['meets this expectation'], (actual) { if (_expectationIsMet(actual)) return null; return Rejection(which: ['does not meet this expectation']); }); } Subject<Foo> get someDerivedValue => context.nest('has someDerivedValue', (actual) { if (_cannotReadDerivedValue(actual)) { return Extracted.rejection(which: ['cannot read someDerivedValue']); } return Extracted.value(_readDerivedValue(actual)); }); // for field reads that will not get rejected, use `has` Subject<Bar> get someField => has((a) => a.someField, 'someField'); }
Add a dev_dependency
on checks: ^0.1.0
.
Replace the existing package:test/test.dart
import with package:test/scaffolding.dart
.
Add an import to package:checks/checks.dart
.
For an incremental migration within the test, add an import to package:test/expect.dart
. Remove it to surface errors in tests that still need to be migrated, or keep it in so the tests work without being fully migrated.
Migrate the test cases.
Replace calls to expect
with a call to checkThat
passing the first argument. When a direct replacement is available, change the second argument from calling a function returning a Matcher, to calling the extension method on the Subject
.
When a non-matcher argument is used for the expected value, it would have been wrapped with equals
automatically. See below, .equals
may not always be the correct replacement in package:checks
.
expect(actual, expected); checkThat(actual).equals(expected); // or maybe checkThat(actual).deepEquals(expected);
equals
Matcher performed a deep equality check on collections. .equals()
expectation will only correspond to [operator ==] so some tests may need to replace .equals()
with .deepEquals()
.