Add NotThrowAfter for Func<Task>

Src/FluentAssertions/Specialized/AsyncFunctionAssertions.cs

@@ -174,6 +174,115 @@ private static void NotThrow(Exception exception, string because, object[] becau
             }
         }
 
+        /// <summary>
+        /// Asserts that the current <see cref="Func{T}"/> stops throwing any exception
+        /// after a specified amount of time.
+        /// </summary>
+        /// <remarks>
+        /// The <see cref="Func{T}"/> 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 after which the <see cref="Func{T}"/> should have stopped throwing any exception.
+        /// </param>
+        /// <param name="pollInterval">
+        /// The time between subsequent invocations of the <see cref="Func{T}"/>.
+        /// </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(TimeSpan waitTime, TimeSpan pollInterval, string because = "", params object[] becauseArgs)
+        {
+            if (waitTime < TimeSpan.Zero)
+            {
+                throw new ArgumentOutOfRangeException(nameof(waitTime), $"The value of {nameof(waitTime)} must be non-negative.");
+            }
+
+            if (pollInterval < TimeSpan.Zero)
+            {
+                throw new ArgumentOutOfRangeException(nameof(pollInterval), $"The value of {nameof(pollInterval)} must be non-negative.");
+            }
+
+
+            TimeSpan? invocationEndTime = null;
+            Exception exception = null;
+            var watch = Stopwatch.StartNew();
+
+            while (invocationEndTime is null || invocationEndTime < waitTime)
+            {
+                exception = InvokeSubjectWithInterception();
+                if (exception is null)
+                {
+                    return;
+                }
+                Task.Delay(pollInterval).Wait();
+                invocationEndTime = watch.Elapsed;
+            }
+            Execute.Assertion
+                .BecauseOf(because, becauseArgs)
+                .FailWith("Did not expect any exceptions after {0}{reason}, but found {1}.", waitTime, exception);
+        }
+
+        /// <summary>
+        /// Asserts that the current <see cref="Func{T}"/> stops throwing any exception
+        /// after a specified amount of time.
+        /// </summary>
+        /// <remarks>
+        /// The <see cref="Func{T}"/> 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 after which the <see cref="Func{T}"/> should have stopped throwing any exception.
+        /// </param>
+        /// <param name="pollInterval">
+        /// The time between subsequent invocations of the <see cref="Func{T}"/>.
+        /// </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 async Task NotThrowAfterAsync(TimeSpan waitTime, TimeSpan pollInterval, string because = "", params object[] becauseArgs)
+        {
+            if (waitTime < TimeSpan.Zero)
+            {
+                throw new ArgumentOutOfRangeException(nameof(waitTime), $"The value of {nameof(waitTime)} must be non-negative.");
+            }
+
+            if (pollInterval < TimeSpan.Zero)
+            {
+                throw new ArgumentOutOfRangeException(nameof(pollInterval), $"The value of {nameof(pollInterval)} must be non-negative.");
+            }
+
+
+            TimeSpan? invocationEndTime = null;
+            Exception exception = null;
+            var watch = Stopwatch.StartNew();
+
+            while (invocationEndTime is null || invocationEndTime < waitTime)
+            {
+                exception = await InvokeSubjectWithInterceptionAsync();
+                if (exception is null)
+                {
+                    return;
+                }
+                await Task.Delay(pollInterval);
+                invocationEndTime = watch.Elapsed;
+            }
+            Execute.Assertion
+                .BecauseOf(because, becauseArgs)
+                .FailWith("Did not expect any exceptions after {0}{reason}, but found {1}.", waitTime, exception);
+	}
         private static Exception GetFirstNonAggregateException(Exception exception)
         {
             Exception nonAggregateException = exception;