Merge pull request #469 from hedgehogqa/add-ignore-combinator

Add Property.ignoreResult combinator

Author: AlexeyRaga

src/Hedgehog/Linq/Property.fs

@@ -96,6 +96,27 @@ type PropertyExtensions private () =
     static member TryWith (property : Property<'T>, onError : Func<exn, Property<'T>>) : Property<'T> =
         Property.tryWith onError.Invoke property
 
+    /// <summary>
+    /// Discards the result of a property, converting it to <see cref="Property"/>.
+    /// This is useful when using assertion libraries that return non-unit types (e.g., fluent assertions).
+    /// Note: The assertion must throw an exception on failure for the property to fail.
+    /// Assertions that throw exceptions will still cause the property to fail.
+    /// </summary>
+    /// <param name="property">The property whose result should be ignored.</param>
+    /// <returns>A property that produces unit.</returns>
+    /// <example>
+    /// <code>
+    /// var property =
+    ///     from x in Gen.Int32(Range.Linear(0, 100)).ForAll()
+    ///     select x.Should().Be(42); // Returns IAssertion
+    /// 
+    /// property.IgnoreResult().Check(); // Convert to <see cref="Property"/> and run
+    /// </code>
+    /// </example>
+    [<Extension>]
+    static member IgnoreResult (property : Property<'T>) : Property =
+        property |> Property.ignoreResult |> Property
+
     [<Extension>]
     static member Report (property : Property) : Report =
         let (Property property) = property

src/Hedgehog/Property.fs

@@ -181,6 +181,12 @@ module Property =
     let internal set (a: 'a) (property : Property<'b>) : Property<'a> =
         property |> map (fun _ -> a)
 
+    /// Discards the result of a property, converting it to Property<unit>.
+    /// This is useful when using assertion libraries that return non-unit types (e.g., fluent assertions).
+    /// Assertions that throw exceptions will still cause the property to fail.
+    let ignoreResult (property : Property<'a>) : Property<unit> =
+        property |> map (fun _ -> ())
+
     // Helper to handle Failure/Discard cases in bind - just wrap and return without calling continuation.
     // Note: Failure and Discard don't carry values, so we can safely change the type parameter.
     let private shortCircuit (journal : Journal) (outcome : Outcome<'a>) : Gen<Lazy<PropertyResult<'b>>> =

tests/Hedgehog.Linq.Tests/LinqTests.cs

@@ -302,5 +302,42 @@ from subset in Gen.SubsetOf(distinctOriginal).ForAll()
 
             prop.Check();
         }
+
+        // Test record to simulate fluent assertion library
+        private record AssertionResult(bool Success);
+
+        private static AssertionResult ShouldBe(int expected, int actual)
+        {
+            if (actual == expected)
+                return new AssertionResult(true);
+            throw new Exception($"Expected {expected} but got {actual}");
+        }
+
+        [Fact]
+        public void IgnoreResult_ConvertsNonUnitPropertyToUnit()
+        {
+            var testRan = false;
+            var property =
+                from x in Gen.Int32(Range.Constant(42, 42)).ForAll()
+                let _ = testRan = true
+                select ShouldBe(42, x); // Returns AssertionResult, not unit
+
+            // Should compile and run
+            property.IgnoreResult().Check();
+            
+            Assert.True(testRan);
+        }
+
+        [Fact]
+        public void IgnoreResult_PreservesFailures()
+        {
+            var property =
+                from x in Gen.Int32(Range.Constant(42, 42)).ForAll()
+                select ShouldBe(99, x); // Will throw
+
+            var report = property.IgnoreResult().Report();
+            
+            Assert.True(report.Status.IsFailed);
+        }
     }
 }

tests/Hedgehog.Tests/Hedgehog.Tests.fsproj

@@ -20,6 +20,7 @@
     <Compile Include="ReportTests.fs" />
     <Compile Include="PropertyTests.fs" />
     <Compile Include="PropertyBindTests.fs" />
+    <Compile Include="TryWithTryFinallyTests.fs" />
     <Compile Include="AsyncTests.fs" />
     <Compile Include="AsyncAndTaskTests.fs" />
     <Compile Include="Program.fs" />

tests/Hedgehog.Tests/Program.fs

@@ -17,6 +17,7 @@ let allTests = testList "All tests" [
     ReportTests.reportTests
     PropertyTests.propertyTests
     PropertyBindTests.propertyBindTests
+    TryWithTryFinallyTests.tryWithTryFinallyTests
     PropertyAsyncTests.asyncTests
 #if !FABLE_COMPILER
     PropertyAsyncAndTaskTests.asyncAndTaskTests

tests/Hedgehog.Tests/TryWithTryFinallyTests.fs

@@ -0,0 +1,66 @@
+module Hedgehog.Tests.TryWithTryFinallyTests
+
+open Hedgehog
+open Hedgehog.FSharp
+open TestDsl
+
+// Simulate fluent assertion library for testing
+type AssertionResult = { Success: bool }
+let shouldBe expected actual =
+    if actual = expected then { Success = true }
+    else failwithf $"Expected %d{expected} but got %d{actual}"
+
+/// Tests for Property.tryFinally and Property.ignoreResult
+let tryWithTryFinallyTests = testList "Property.tryFinally and ignoreResult tests" [
+    
+    testCase "tryFinally cleanup runs on success" <| fun () ->
+        let mutable cleanupCalled = false
+        property {
+            let! x = Gen.constant 42
+            return x = 42
+        }
+        |> Property.tryFinally (fun () -> cleanupCalled <- true)
+        |> Property.checkBool
+
+        Expect.isTrue cleanupCalled
+    
+    testCase "tryFinally cleanup runs on failure" <| fun () ->
+        let mutable cleanupCalled = false
+        let report =
+            property {
+                let! x = Gen.constant 42
+                return false
+            }
+            |> Property.tryFinally (fun () -> cleanupCalled <- true)
+            |> Property.reportBool
+
+        match report.Status with
+        | Failed _ -> ()
+        | _ -> failwith "Expected Failed status"
+
+        Expect.isTrue cleanupCalled
+    
+    testCase "ignoreResult converts Property<'a> to Property<unit>" <| fun () ->
+        let mutable testRan = false
+        property {
+            let! x = Gen.constant 42
+            testRan <- true
+            return shouldBe 42 x  // Returns AssertionResult
+        }
+        |> Property.ignoreResult  // Convert to Property<unit>
+        |> Property.check
+
+    
+    testCase "ignoreResult preserves failures" <| fun () ->
+        let report =
+            property {
+                let! x = Gen.constant 42
+                return shouldBe 99 x  // Will throw
+            }
+            |> Property.ignoreResult
+            |> Property.report
+
+        match report.Status with
+        | Failed _ -> ()
+        | _ -> failwith "Expected Failed status"
+]