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I am new to unit testing and trying to understand how WillRaise works in DUnitX. In the simple example below, there is only 1 function being tested: it is given an integer it expects the given integer to be positive so raises EMySimpleException if it is zero or less otherwise, it just returns the given integer. The first two TestCases check the return value. One of them passes and one of them fails (which is correct). The next 2 TestCases use WillRaise to check if the correct exception is raised for a negative input. I expect one test to pass and one to fail - but they both pass and I don't understand why. I am assuming that I do not yet fully understand how to use WillRaise. Perhaps someone can point out my stupid error? The code being tested: unit MySimpleLogic; interface uses System.SysUtils; type EMySimpleException = class(Exception) public constructor Create(const Msg: string); overload; end; TMySimpleObject = class public function SimpleFunctionRequiringPositiveInput(const AValue: integer): integer; end; implementation { MySimpleObject } function TMySimpleObject.SimpleFunctionRequiringPositiveInput(const AValue: integer): integer; begin if (AValue <= 0) then raise EMySimpleException.Create('Negative input not allowed'); result := Avalue; end; { EMySimpleException } constructor EMySimpleException.Create(const Msg: string); begin inherited Create(Msg); end; end. The unit testing code: unit TestsForMySimpleLogic; interface uses System.SysUtils, DUnitX.TestFramework, MySimpleLogic; type [TestFixture] TMyTestObject = class private CUT: TMySimpleObject; public [Setup] procedure Setup; [TearDown] procedure TearDown; [Test] [TestCase('TestPositiveInput01','1,1')] [TestCase('TestPositiveInput02','1,2')] procedure TestPositiveInput(const AValue: integer; const Expected: integer); [Test] [TestCase('NegativeValueShouldRaiseEMySimpleException', '-1,EMySimpleException')] [TestCase('NegativeValueShouldRaiseESomeOtherException', '-2,ESomeOtherException')] procedure RaiseExceptionForNegativeInput(const AValue: integer; const exceptionClass : ExceptClass); end; implementation procedure TMyTestObject.TestPositiveInput(const AValue: integer; const Expected: integer); begin var Actual := CUT.SimpleFunctionRequiringPositiveInput(AValue); Assert.AreEqual(Expected, Actual); end; procedure TMyTestObject.RaiseExceptionForNegativeInput(const AValue: integer; const exceptionClass : ExceptClass); begin var TestMethod: TTestLocalMethod := procedure begin CUT.SimpleFunctionRequiringPositiveInput(AValue); end; Assert.WillRaise(TestMethod, exceptionClass, 'Incorrect Exception raised'); end; procedure TMyTestObject.Setup; begin CUT := TMySimpleObject.Create; end; procedure TMyTestObject.TearDown; begin CUT.Free; end; initialization TDUnitX.RegisterTestFixture(TMyTestObject); end.