Add some tests for RetryUtility (#1296)

* Add some tests for RetryUtility
* Add another test and method documentation

SIL.Core.Tests/Code/RetryUtilityTests.cs

@@ -1,17 +1,11 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 using NUnit.Framework;
 using SIL.Code;
 
 namespace SIL.Tests.Code
 {
-	/// <summary>
-	/// This is a work in progress. At this point it only has a test for one recently-added bit of functionality.
-	/// </summary>
 	public class RetryUtilityTests
 	{
 		[Test]
@@ -23,5 +17,78 @@ public void TypesIncludes_MainClassAndSubclasses_ButNotSuperclass()
 			Assert.That(RetryUtility.TypesIncludes(types, typeof(FileNotFoundException)), Is.True);
 			Assert.That(RetryUtility.TypesIncludes(types, typeof(SystemException)), Is.False);
 		}
+
+		[Test]
+		public void Retry_WorksOnFirstAttempt()
+		{
+			var n = 0;
+			RetryUtility.Retry(() => { n++; }, 3, 1);
+			Assert.That(n, Is.EqualTo(1));
+		}
+
+		[Test]
+		public void Retry_WorksOnSecondAttempt()
+		{
+			var n = 0;
+			RetryUtility.Retry(() => {
+				n++;
+				if (n == 1)
+					throw new ApplicationException();
+			}, 3, 1, new HashSet<Type> (new[] { typeof(Exception) }));
+			Assert.That(n, Is.EqualTo(2));
+		}
+
+		[Test]
+		public void Retry_StopsAfter3Attempts()
+		{
+			var n = 0;
+			Assert.That(() => RetryUtility.Retry(() => {
+				n++;
+				throw new ApplicationException();
+			}, 3, 1, new HashSet<Type> (new[] { typeof(Exception) })), Throws.Exception.TypeOf<ApplicationException>());
+			Assert.That(n, Is.EqualTo(3));
+		}
+
+		[Test]
+		public void Retry_NoWorkFor0Attempts()
+		{
+			var n = 0;
+			RetryUtility.Retry(() => { n++; }, 0, 1);
+			Assert.That(n, Is.EqualTo(0));
+		}
+
+		[Test]
+		public void Retry_NoRetriesWithoutExceptionType()
+		{
+			var n = 0;
+			Assert.That(() => RetryUtility.Retry(() => {
+				n++;
+				throw new ApplicationException();
+			}, 3, 1, null), Throws.Exception.TypeOf<ApplicationException>());
+			Assert.That(n, Is.EqualTo(1));
+		}
+
+		[Test]
+		public void Retry_DefaultsToIOException()
+		{
+			var n = 0;
+			Assert.That(() => RetryUtility.Retry(() => {
+				n++;
+				throw new IOException();
+			}, 3, 1, null), Throws.Exception.TypeOf<IOException>());
+			Assert.That(n, Is.EqualTo(3));
+		}
+
+		[Test]
+		public void Retry_CatchesSpecifiedExceptionsOnly()
+		{
+			var n = 0;
+			Assert.That(() => RetryUtility.Retry(() => {
+				n++;
+				throw new Exception();
+			}, 3, 1, new HashSet<Type> (new[] { typeof(ApplicationException) })),
+				Throws.Exception.TypeOf<Exception>());
+			Assert.That(n, Is.EqualTo(1));
+		}
 	}
 }

SIL.Core/Code/RetryUtility.cs

@@ -31,6 +31,21 @@ public static void Retry(Action action, int maxRetryAttempts = kDefaultMaxRetryA
 			}, maxRetryAttempts, retryDelay, exceptionTypesToRetry, memo);
 		}
 
+		/// <summary>
+		/// Retry <paramref name="action"/> up to <paramref name="maxRetryAttempts"/> times if it
+		/// throws one of the exceptions in <paramref name="exceptionTypesToRetry"/> or a subclassed
+		/// exception. The default value for <paramref name="exceptionTypesToRetry"/> is null which
+		/// will catch <c>IOException</c>s.
+		/// </summary>
+		/// <param name="action">The action to run</param>
+		/// <param name="maxRetryAttempts">Number of attempts to run <paramref name="action"/></param>
+		/// <param name="retryDelay">Delay in milliseconds between attempts</param>
+		/// <param name="exceptionTypesToRetry">Exceptions to catch and retry. Not listed exceptions
+		/// are thrown.</param>
+		/// <param name="memo">Text to append to the debug message in case of
+		/// <paramref name="action"/> throwing an exception.</param>
+		/// <typeparam name="T">Type that <paramref name="action"/> returns</typeparam>
+		/// <returns>Return value of <paramref name="action"/></returns>
 		public static T Retry<T>(Func<T> action, int maxRetryAttempts = kDefaultMaxRetryAttempts, int retryDelay = kDefaultRetryDelay, ISet<Type> exceptionTypesToRetry = null, string memo = "")
 		{
 			if (exceptionTypesToRetry == null)