Add Should().NotThrowAfter assertion for actions

Src/FluentAssertions/Specialized/ActionAssertions.cs

@@ -4,7 +4,7 @@
 using System.Linq;
 using System.Reflection;
 using System.Runtime.CompilerServices;
-
+using System.Threading.Tasks;
 using FluentAssertions.Common;
 using FluentAssertions.Execution;
 using FluentAssertions.Primitives;
@@ -114,6 +114,54 @@ public void NotThrow(string because = "", params object[] becauseArgs)
             }
         }
 
+        /// <summary>
+        /// Asserts that the current <see cref="Action"/> stops throwing any exception
+        /// after a specified amount of time.
+        /// </summary>
+        /// <remarks>
+        /// The <see cref="Action"/> is invoked. If it raises an exception,
+        /// the invocation is repeated until it either stops raising any exceptions
+        /// or the specified wait time is exceeded.
+        /// </remarks>
+        /// <param name="waitTime">
+        /// The time in milliseconds after which the <see cref="Action"/> should have stopped throwing any exception.
+        /// </param>
+        /// <param name="pollInterval">
+        /// The time between subsequent invocations of the <see cref="Action"/>.
+        /// </param>
+        /// <param name="because">
+        /// A formatted phrase as is supported by <see cref="string.Format(string,object[])" /> explaining why the assertion
+        /// is needed. If the phrase does not start with the word <i>because</i>, it is prepended automatically.
+        /// </param>
+        /// <param name="becauseArgs">
+        /// Zero or more objects to format using the placeholders in <see cref="because" />.
+        /// </param>
+        /// <exception cref="ArgumentOutOfRangeException">Throws if waitTime or pollInterval are negative.</exception>
+        public void NotThrowAfter(int waitTime, int pollInterval, string because = "", params object[] becauseArgs)
+        {
+            FailIfSubjectIsAsyncVoid();
+
+            if(waitTime < 0 || pollInterval < 0)
+                throw new ArgumentOutOfRangeException("The values of waitTime and pollInterval must be positive.");
+
+            var watch = Stopwatch.StartNew();
+            long invocationEndTime = -1;
+            Exception exception = null;
+
+            while (invocationEndTime < waitTime)
+            {
+                exception = InvokeSubjectWithInterception();
+                if (exception is null)
+                    return;
+
+                Task.Delay(pollInterval).Wait();
+                invocationEndTime = watch.ElapsedMilliseconds;
+            }
+            Execute.Assertion
+                        .BecauseOf(because, becauseArgs)
+                        .FailWith("Did not expect any exception after {0} milliseconds{reason}, but found {1}.", waitTime, exception);
+        }
+
         private Exception InvokeSubjectWithInterception()
         {
             Exception actualException = null;

Tests/Shared.Specs/ExceptionAssertionSpecs.cs

@@ -1,10 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using Xunit;
 using Xunit.Sdk;
-
 using FakeItEasy;
-
 using FluentAssertions.Primitives;
 
 namespace FluentAssertions.Specs
@@ -895,6 +894,62 @@ public void When_no_exception_should_be_thrown_and_none_was_it_should_not_throw(
             //-----------------------------------------------------------------------------------------------------------
             foo.Invoking(f => f.Do()).Should().NotThrow();
         }
+
+        private static void ThrowUntil(Stopwatch watch, int throwTime)
+        {
+                if(watch.ElapsedMilliseconds <= throwTime)
+                    throw new ArgumentException("An exception was forced");
+        }
+
+        [Fact]
+        public void When_no_exception_should_be_thrown_after_wait_time_but_it_was_it_should_throw()
+        {
+            //-----------------------------------------------------------------------------------------------------------
+            // Arrange
+            //-----------------------------------------------------------------------------------------------------------
+            var foo = A.Fake<IFoo>();
+            var watch = Stopwatch.StartNew();
+            var waitTime = 100;
+            var pollInterval = 10;
+
+            void ThrowLongerThanWaitTime() => ThrowUntil(watch, waitTime + waitTime / 2);
+
+            A.CallTo(() => foo.Do()).Invokes(ThrowLongerThanWaitTime);
+            //-----------------------------------------------------------------------------------------------------------
+            // Act
+            //-----------------------------------------------------------------------------------------------------------
+            Action action = () => foo.Invoking(f => f.Do())
+                                     .Should().NotThrowAfter(waitTime, pollInterval, "we passed valid arguments");
+
+            //-----------------------------------------------------------------------------------------------------------
+            // Assert
+            //-----------------------------------------------------------------------------------------------------------
+            action
+                .Should().Throw<XunitException>()
+                         .Where(e => e.Message.Contains(
+					 "Did not expect any exception after 100 milliseconds because we passed valid " +
+					 "arguments, but found FakeItEasy.UserCallbackException")); }
+
+        [Fact]
+        public void When_no_exception_should_be_thrown_after_wait_time_and_none_was_it_should_not_throw()
+        {
+            //-----------------------------------------------------------------------------------------------------------
+            // Arrange
+            //-----------------------------------------------------------------------------------------------------------
+            var foo = A.Fake<IFoo>();
+            var watch = Stopwatch.StartNew();
+            var waitTime = 100;
+            var pollInterval = 10;
+
+            void ThrowShorterThanWaitTime() => ThrowUntil(watch, waitTime / 2);
+
+            A.CallTo(() => foo.Do()).Invokes(ThrowShorterThanWaitTime);
+            //-----------------------------------------------------------------------------------------------------------
+            // Act / Assert
+            //-----------------------------------------------------------------------------------------------------------
+            foo.Invoking(f => f.Do()).Should().NotThrowAfter(waitTime, pollInterval);
+        }
+
     }
 
     #endregion