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<h2>Constraint-Based Assert Model (NUnit 2.4)</h2>
<p>The constraint-based Assert model uses a single method of the Assert class
for all assertions. The logic necessary to carry out each assertion is
embedded in the constraint object passed as the second parameter to that
method.
<p>Here's a very simple assert using the constraint model:
<pre> Assert.That( myString, Is.EqualTo("Hello") );</pre>
<p>The second argument in this assertion uses one of NUnit's <b>syntax helpers</b>
to create an <b>EqualConstraint</b>. The same assertion could also be made in this form:
<pre> Assert.That( myString, new EqualConstraint("Hello") );</pre>
<p>Using this model, all assertions are made using one of the forms of the
Assert.That() method, which has a number of overloads...
<div class="code" style="width: 36em">
<pre>Assert.That( object actual, IConstraint constraint )
Assert.That( object actual, IConstraint constraint, string message )
Assert.That( object actual, IConstraint constraint, string message,
object[] parms )
Assert.That( bool condition );
Assert.That( bool condition, string message );
Assert.That( bool condition, string message, object[] parms );</pre>
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<p>If you derive your test fixture class from <b>AssertionHelper</b>, the
Expect() method may be used in place of Assert.That()...
<div class="code" style="width: 36em">
<pre>Expect( object actual, IConstraint constraint )
Expect( object actual, IConstraint constraint, string message )
Expect( object actual, IConstraint constraint, string message,
object[] parms )
Expect( bool condition );
Expect( bool condition, string message );
Expect( bool condition, string message, object[] parms );</pre>
</div>
<p>The overloads that take a bool work exactly like Assert.IsTrue.
<p>For overloads taking a constraint, the argument must be a object implementing
the <b>IConstraint</b> interface, which supports performing a test
on an actual value and generating appropriate messages. This interface
is described in more detail under
<a href="customConstraints.html">Custom Constraints</a>.
<p>NUnit provides a number of constraint classes similar to the <b>EqualConstraint</b>
used in the example above. Generally, these classes may be used directly or
through a syntax helper. Test fixture classes inheriting from <b>AssertionHelper</b>
are able to use shorter forms. The valid forms are described on the pages related to
each constraint. Note that the menu items listed to the right generally reflect the
names of the syntax helpers.
<p><b>See also:</b> the
<a href="classicModel.html">classic model</a> of assertions.
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