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 <h3>TheoryAttribute (NUnit 2.5) (Experimental)</h3>

 <p>A Theory is a special type of test, used to verify a general
    statement about the system under development. Normal tests are
    <em>example-based</em>. That is, the developer supplies one or
    more examples of inputs and expected outputs either within the
    code of the test or - in the case of
    <a href="parameterizedTests.html">Parameterized Tests</a>
    - as arguments to the test method. A theory, on the other hand,
    makes a general statement that all of its assertions will pass
    for all arguments satisfying certain assumptions.

 <p>Theories are implemented in NUnit
    as methods within a <b>TestFixture</b>, which are annotated
    with the <b>TheoryAttribute</b>. Theory methods must always have
    arguments and therefore appears quite similar to
    <a href="parameterizedTests.html">Parameterized Tests</a>   at first glance. However, a Theory incorporates additional data sources
    for its arguments and allows special processing for assumptions
    about that data. The key difference, though, is that theories
    make general statements and are more than just a set of examples.

 <h4>Data for Theories</h4>

 <p>The primary source of data for a <b>Theory</b> is the
    <a href="datapoint.html"><b>Datapoint</b> or <b>Datapoints</b> attribute</a>.
    NUnit will use any fields of the required types, which are annotated
    with one of these attributes, to provide data for each parameter
    of the Theory. NUnit assembles the values for individual arguments
    combinatorially to provide test cases for the theory.

 <p>In addition to the Datapoint and Datapoints attributes, it
    is possible to use any of the approaches for supplying data
    that are recognized on normal parameterized tests. We suggest
    that this capability not be overused, since it runs counter
    to the distinction between a test based on examples and a
    theory. However, it may be useful in order to guarantee that
    a specific test case is included.

 <h4>Assumptions</h4>

 <p>The theory itself is responsible for ensuring that all data supplied
    meets its assumptions. It does this by use of the
    <b>Assume.That(...)</b> construct, which works just like
    <b>Assert.That(...)</b> but does not cause a failure. If
    the assumption is not satisfied for a particular test case, that case
    returns an Inconclusive result, rather than a Success or Failure.

 <p>The overall result of executing a Theory over a set of test cases is
    determined as follows:

    <ul>
    <li>If the assumptions are violated for <b>all</b> test cases, then the
        Theory itself is marked as a failure.

    <li>If any Assertion fails, the Theory itself fails.

    <li>If at least <b>some</b> cases pass the stated assumptions, and
        there are <b>no</b> assertion failures or exceptions, then the
 	   Theory passes.
    </ul>

 <h4>Example:</h4>

 <p>In the following example, the theory SquareRootDefinition
    verifies that the implementation of square root satisies
    the following definition:

 <p style="margin: 2em"><i>
 "Given a non-negative number, the square root of that number
  is always non-negative and, when multiplied by itself, gives
  the original number."</i>

 <div class="code" style="width: 36em">
 <pre>
 public class SqrtTests
 {
     [Datapoints]
     public double[] values = new double[] { 0.0, 1.0, -1.0, 42.0 };

     [Theory]
     public void SquareRootDefinition(double num)
     {
         Assume.That(num >= 0.0);

         double sqrt = Math.Sqrt(num);

         Assert.That(sqrt >= 0.0);
         Assert.That(sqrt * sqrt, Is.EqualTo(num).Within(0.000001));
     }
 }
 </pre>
 </div>

 <h4>See also...</h4>

 <ul>
 <li><a href="datapoint.html">Datapoint(s)Attribute</a><li><a href="parameterizedTests.html">Parameterized Tests</a></ul>

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	<h3>TheoryAttribute (NUnit 2.5) (Experimental)</h3>

	<p>A Theory is a special type of test, used to verify a general
	statement about the system under development. Normal tests are
	<em>example-based</em>. That is, the developer supplies one or
	more examples of inputs and expected outputs either within the
	code of the test or - in the case of
	<a href="parameterizedTests.html">Parameterized Tests</a>
	- as arguments to the test method. A theory, on the other hand,
	makes a general statement that all of its assertions will pass
	for all arguments satisfying certain assumptions.

	<p>Theories are implemented in NUnit
	as methods within a <b>TestFixture</b>, which are annotated
	with the <b>TheoryAttribute</b>. Theory methods must always have
	arguments and therefore appears quite similar to
	<a href="parameterizedTests.html">Parameterized Tests</a> at first glance. However, a Theory incorporates additional data sources
	for its arguments and allows special processing for assumptions
	about that data. The key difference, though, is that theories
	make general statements and are more than just a set of examples.

	<h4>Data for Theories</h4>

	<p>The primary source of data for a <b>Theory</b> is the
	<a href="datapoint.html"><b>Datapoint</b> or <b>Datapoints</b> attribute</a>.
	NUnit will use any fields of the required types, which are annotated
	with one of these attributes, to provide data for each parameter
	of the Theory. NUnit assembles the values for individual arguments
	combinatorially to provide test cases for the theory.

	<p>In addition to the Datapoint and Datapoints attributes, it
	is possible to use any of the approaches for supplying data
	that are recognized on normal parameterized tests. We suggest
	that this capability not be overused, since it runs counter
	to the distinction between a test based on examples and a
	theory. However, it may be useful in order to guarantee that
	a specific test case is included.

	<h4>Assumptions</h4>

	<p>The theory itself is responsible for ensuring that all data supplied
	meets its assumptions. It does this by use of the
	<b>Assume.That(...)</b> construct, which works just like
	<b>Assert.That(...)</b> but does not cause a failure. If
	the assumption is not satisfied for a particular test case, that case
	returns an Inconclusive result, rather than a Success or Failure.

	<p>The overall result of executing a Theory over a set of test cases is
	determined as follows:

	<ul>
	<li>If the assumptions are violated for <b>all</b> test cases, then the
	Theory itself is marked as a failure.

	<li>If any Assertion fails, the Theory itself fails.

	<li>If at least <b>some</b> cases pass the stated assumptions, and
	there are <b>no</b> assertion failures or exceptions, then the
	Theory passes.
	</ul>

	<h4>Example:</h4>

	<p>In the following example, the theory SquareRootDefinition
	verifies that the implementation of square root satisies
	the following definition:

	<p style="margin: 2em"><i>
	"Given a non-negative number, the square root of that number
	is always non-negative and, when multiplied by itself, gives
	the original number."</i>

	<div class="code" style="width: 36em">
	<pre>
	public class SqrtTests
	{
	[Datapoints]
	public double[] values = new double[] { 0.0, 1.0, -1.0, 42.0 };

	[Theory]
	public void SquareRootDefinition(double num)
	{
	Assume.That(num >= 0.0);

	double sqrt = Math.Sqrt(num);

	Assert.That(sqrt >= 0.0);
	Assert.That(sqrt * sqrt, Is.EqualTo(num).Within(0.000001));
	}
	}
	</pre>
	</div>

	<h4>See also...</h4>

	<ul>
	<li><a href="datapoint.html">Datapoint(s)Attribute</a><li><a href="parameterizedTests.html">Parameterized Tests</a></ul>

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