Allows test overrides of Dialogflow retry delay (#292)

The current retry delay of 30 seconds is causing a significant delay when running unit tests that exercise that retry delay. This change allows the delay duration to be overridden.

src/NLU.DevOps.Dialogflow.Tests/DialogflowNLUTestClientTests.cs

@@ -24,6 +24,21 @@ internal static class DialogflowNLUTestClientTests
     {
         private const double Epsilon = 1e-6;
 
+        private static TimeSpan originalThrottle;
+
+        [OneTimeSetUp]
+        public static void SetUp()
+        {
+            originalThrottle = DialogflowNLUTestClient.ThrottleQueryDelay;
+            DialogflowNLUTestClient.ThrottleQueryDelay = TimeSpan.FromMilliseconds(100);
+        }
+
+        [OneTimeTearDown]
+        public static void TearDown()
+        {
+            DialogflowNLUTestClient.ThrottleQueryDelay = originalThrottle;
+        }
+
         [Test]
         public static void ThrowsArgumentNull()
         {

src/NLU.DevOps.Dialogflow/DialogflowNLUTestClient.cs

@@ -29,9 +29,6 @@ internal sealed class DialogflowNLUTestClient : DefaultNLUTestClient
         private const string DialogflowProjectIdConfigurationKey = "dialogflowProjectId";
         private const string DialogflowSessionIdConfigurationKey = "dialogflowSessionId";
 
-        // Dialogflow typically limits the number of requests per minute, so setting a retry delay to 30 seconds.
-        private static readonly TimeSpan ThrottleQueryDelay = TimeSpan.FromSeconds(30);
-
         private SessionsClient sessionsClient;
 
         public DialogflowNLUTestClient(SessionsClient sessionsClient, IConfiguration configuration)
@@ -45,6 +42,9 @@ public DialogflowNLUTestClient(IConfiguration configuration)
             this.Configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
         }
 
+        // Dialogflow typically limits the number of requests per minute, so setting a retry delay to 30 seconds.
+        internal static TimeSpan ThrottleQueryDelay { get; set; } = TimeSpan.FromSeconds(30);
+
         private static ILogger Logger => LazyLogger.Value;
 
         private static Lazy<ILogger> LazyLogger { get; } = new Lazy<ILogger>(() => ApplicationLogger.LoggerFactory.CreateLogger<DialogflowNLUTestClient>());