The NUnit Constraint syntax has been re-implemented based on Generic methods to avoid boxing and provide greater type safety. Improvements are ongoing work is ongoing in this area. The following table lists constraints, which are currently supported. New constraints are added on an ongoing basis.

The "Expression Syntax" column shows how the constraint is created while parsing a constraint expression. For constraints that may begin an expression, the "Initial Syntax" column shows the syntax used to initialize the expression. Note that some constraints have been developed and tested but do not yet have syntax elements defined.

Constraint Expression Syntax Initial Syntax
AllItemsConstraint All Is.All, Has.All
AndConstraint And
CollectionEquivalentConstraint EquivalentTo Is.EquivalentTo
EmptyCollectionConstraint Empty Is.Empty
EmptyConstraint Empty Is.Empty
EmptyStringConstraint Empty Is.Empty
EqualConstraint EqualTo Is.EqualTo
Zero Is.Zero
ExactTypeConstraint TypeOf Is.TypeOf
FalseConstraint False Is.False
GreaterThanConstraint GreaterThan Is.GreaterThan
Positive Is.Positive
GreaterThanOrEqualConstraint GreaterThanOrEqual Is.GreaterThanOrEqual
AtLeast Is.AtLeast
InstanceOfTypeConstraint InstanceOf Is.InstanceOf
LessThanConstraint LessThan Is.LessThan
Negative Is.Negative
LessThanOrEqualConstraint LessThanOrEqual Is.LessThanOrEqual
AtMost Is.AtMost
NoItemConstraint None Has.None, Has.No
NotConstraint Not Is.Not
NullConstraint Null Is.Null
OrConstraint Or
SameAsConstraint SameAs Is.SameAs
SomeItemsConstraint Some Has.Some, Contains.Item
SubstringConstraint Substring Contains.Substring
ThrowsConstraint Throws.TypeOf
ThrowsExceptionConstraint Throws.Exception
ThrowsNothingConstraint Throws.Nothing
TrueConstraint True Is.True
UniqueItemsConstraint Unique Is.Unique