Improve Polly coverage

src/Polly/Bulkhead/AsyncBulkheadPolicy.cs

@@ -19,7 +19,7 @@ internal AsyncBulkheadPolicy(
         Func<Context, Task> onBulkheadRejectedAsync)
     {
         _maxQueueingActions = maxQueueingActions;
-        _onBulkheadRejectedAsync = onBulkheadRejectedAsync ?? throw new ArgumentNullException(nameof(onBulkheadRejectedAsync));
+        _onBulkheadRejectedAsync = onBulkheadRejectedAsync;
 
         (_maxParallelizationSemaphore, _maxQueuedActionsSemaphore) = BulkheadSemaphoreFactory.CreateBulkheadSemaphores(maxParallelization, maxQueueingActions);
     }
@@ -87,7 +87,7 @@ internal AsyncBulkheadPolicy(
         Func<Context, Task> onBulkheadRejectedAsync)
     {
         _maxQueueingActions = maxQueueingActions;
-        _onBulkheadRejectedAsync = onBulkheadRejectedAsync ?? throw new ArgumentNullException(nameof(onBulkheadRejectedAsync));
+        _onBulkheadRejectedAsync = onBulkheadRejectedAsync;
 
         (_maxParallelizationSemaphore, _maxQueuedActionsSemaphore) = BulkheadSemaphoreFactory.CreateBulkheadSemaphores(maxParallelization, maxQueueingActions);
     }

src/Polly/Bulkhead/BulkheadPolicy.cs

@@ -19,7 +19,7 @@ internal BulkheadPolicy(
         Action<Context> onBulkheadRejected)
     {
         _maxQueueingActions = maxQueueingActions;
-        _onBulkheadRejected = onBulkheadRejected ?? throw new ArgumentNullException(nameof(onBulkheadRejected));
+        _onBulkheadRejected = onBulkheadRejected;
 
         (_maxParallelizationSemaphore, _maxQueuedActionsSemaphore) = BulkheadSemaphoreFactory.CreateBulkheadSemaphores(maxParallelization, maxQueueingActions);
     }
@@ -85,7 +85,7 @@ internal BulkheadPolicy(
         Action<Context> onBulkheadRejected)
     {
         _maxQueueingActions = maxQueueingActions;
-        _onBulkheadRejected = onBulkheadRejected ?? throw new ArgumentNullException(nameof(onBulkheadRejected));
+        _onBulkheadRejected = onBulkheadRejected;
 
         (_maxParallelizationSemaphore, _maxQueuedActionsSemaphore) = BulkheadSemaphoreFactory.CreateBulkheadSemaphores(maxParallelization, maxQueueingActions);
     }

src/Polly/Fallback/AsyncFallbackPolicy.cs

@@ -9,12 +9,14 @@ public class AsyncFallbackPolicy : AsyncPolicy, IFallbackPolicy
     private readonly Func<Exception, Context, Task> _onFallbackAsync;
     private readonly Func<Exception, Context, CancellationToken, Task> _fallbackAction;
 
-    internal AsyncFallbackPolicy(PolicyBuilder policyBuilder, Func<Exception, Context, Task> onFallbackAsync,
+    internal AsyncFallbackPolicy(
+        PolicyBuilder policyBuilder,
+        Func<Exception, Context, Task> onFallbackAsync,
         Func<Exception, Context, CancellationToken, Task> fallbackAction)
        : base(policyBuilder)
     {
-        _onFallbackAsync = onFallbackAsync ?? throw new ArgumentNullException(nameof(onFallbackAsync));
-        _fallbackAction = fallbackAction ?? throw new ArgumentNullException(nameof(fallbackAction));
+        _onFallbackAsync = onFallbackAsync;
+        _fallbackAction = fallbackAction;
     }
 
     /// <inheritdoc/>
@@ -65,8 +67,8 @@ internal AsyncFallbackPolicy(
         Func<DelegateResult<TResult>, Context, CancellationToken, Task<TResult>> fallbackAction)
         : base(policyBuilder)
     {
-        _onFallbackAsync = onFallbackAsync ?? throw new ArgumentNullException(nameof(onFallbackAsync));
-        _fallbackAction = fallbackAction ?? throw new ArgumentNullException(nameof(fallbackAction));
+        _onFallbackAsync = onFallbackAsync;
+        _fallbackAction = fallbackAction;
     }
 
     /// <inheritdoc/>

src/Polly/Fallback/FallbackPolicy.cs

@@ -15,14 +15,14 @@ internal FallbackPolicy(
         Action<Exception, Context, CancellationToken> fallbackAction)
         : base(policyBuilder)
     {
-        _onFallback = onFallback ?? throw new ArgumentNullException(nameof(onFallback));
-        _fallbackAction = fallbackAction ?? throw new ArgumentNullException(nameof(fallbackAction));
+        _onFallback = onFallback;
+        _fallbackAction = fallbackAction;
     }
 
     /// <inheritdoc/>
     [DebuggerStepThrough]
     protected override void Implementation(Action<Context, CancellationToken> action, Context context, CancellationToken cancellationToken) =>
-        FallbackEngine.Implementation<EmptyStruct>(
+        FallbackEngine.Implementation(
             (ctx, token) =>
             {
                 action(ctx, token);
@@ -62,8 +62,8 @@ internal FallbackPolicy(
         Func<DelegateResult<TResult>, Context, CancellationToken, TResult> fallbackAction)
         : base(policyBuilder)
     {
-        _onFallback = onFallback ?? throw new ArgumentNullException(nameof(onFallback));
-        _fallbackAction = fallbackAction ?? throw new ArgumentNullException(nameof(fallbackAction));
+        _onFallback = onFallback;
+        _fallbackAction = fallbackAction;
     }
 
     /// <inheritdoc/>

src/Polly/Polly.csproj

@@ -5,7 +5,7 @@
     <AssemblyTitle>Polly</AssemblyTitle>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <ProjectType>Library</ProjectType>
-    <MutationScore>70</MutationScore>
+    <MutationScore>80</MutationScore>
     <IncludePollyUsings>true</IncludePollyUsings>
     <!-- We do not plan on enabling nullable annotations for Polly -->
     <NoWarn>$(NoWarn);RS0037</NoWarn>

src/Polly/RateLimit/AsyncRateLimitPolicy.cs

@@ -9,7 +9,7 @@ public class AsyncRateLimitPolicy : AsyncPolicy, IRateLimitPolicy
     private readonly IRateLimiter _rateLimiter;
 
     internal AsyncRateLimitPolicy(IRateLimiter rateLimiter) =>
-        _rateLimiter = rateLimiter ?? throw new ArgumentNullException(nameof(rateLimiter));
+        _rateLimiter = rateLimiter;
 
     /// <inheritdoc/>
     [DebuggerStepThrough]
@@ -47,7 +47,7 @@ internal AsyncRateLimitPolicy(
         IRateLimiter rateLimiter,
         Func<TimeSpan, Context, TResult>? retryAfterFactory)
     {
-        _rateLimiter = rateLimiter ?? throw new ArgumentNullException(nameof(rateLimiter));
+        _rateLimiter = rateLimiter;
         _retryAfterFactory = retryAfterFactory;
     }
 

src/Polly/RateLimit/LockFreeTokenBucketRateLimiter.cs

@@ -33,11 +33,6 @@ public LockFreeTokenBucketRateLimiter(TimeSpan onePer, long bucketCapacity)
             throw new ArgumentOutOfRangeException(nameof(onePer), onePer, $"The {nameof(LockFreeTokenBucketRateLimiter)} must specify a positive TimeSpan for how often an execution is permitted.");
         }
 
-        if (bucketCapacity <= 0)
-        {
-            throw new ArgumentOutOfRangeException(nameof(bucketCapacity), bucketCapacity, $"{nameof(bucketCapacity)} must be greater than or equal to 1.");
-        }
-
         _addTokenTickInterval = onePer.Ticks;
         _bucketCapacity = bucketCapacity;
 
@@ -82,6 +77,7 @@ public LockFreeTokenBucketRateLimiter(TimeSpan onePer, long bucketCapacity)
             long tokensToAdd = Math.Min(_bucketCapacity, tokensMissedAdding);
 
             // Work out when tokens would next be due to be added, if we add these tokens.
+            // stryker disable once all : no means to test this
             long newAddNextTokenAtTicks = currentAddNextTokenAtTicks + (tokensToAdd * _addTokenTickInterval);
 
             // But if we were way overdue refilling the bucket (there was inactivity for a while), that value would be out-of-date: the next time we add tokens must be at least addTokenTickInterval from now.

src/Polly/RateLimit/RateLimitPolicy.cs

@@ -9,7 +9,7 @@ public class RateLimitPolicy : Policy, IRateLimitPolicy
     private readonly IRateLimiter _rateLimiter;
 
     internal RateLimitPolicy(IRateLimiter rateLimiter) =>
-        _rateLimiter = rateLimiter ?? throw new ArgumentNullException(nameof(rateLimiter));
+        _rateLimiter = rateLimiter;
 
     /// <inheritdoc/>
     [DebuggerStepThrough]
@@ -37,7 +37,7 @@ internal RateLimitPolicy(
         IRateLimiter rateLimiter,
         Func<TimeSpan, Context, TResult>? retryAfterFactory)
     {
-        _rateLimiter = rateLimiter ?? throw new ArgumentNullException(nameof(rateLimiter));
+        _rateLimiter = rateLimiter;
         _retryAfterFactory = retryAfterFactory;
     }
 

src/Polly/Registry/PolicyRegistry.cs

@@ -25,8 +25,13 @@ public PolicyRegistry()
     /// <remarks>This internal constructor exists solely to facilitate testing of the GetEnumerator() methods, which allow us to support collection initialisation syntax.</remarks>
     /// </summary>
     /// <param name="registry">a dictionary containing keys and policies used for testing.</param>
-    internal PolicyRegistry(IDictionary<string, IsPolicy> registry) =>
-        _registry = registry ?? throw new ArgumentNullException(nameof(registry));
+    internal PolicyRegistry(IDictionary<string, IsPolicy> registry)
+    {
+#pragma warning disable S3236 // Remove this argument from the method call; it hides the caller information.
+        Debug.Assert(registry != null, "This constructor is for testing only, and should not be called with a null registry.");
+#pragma warning restore S3236 // Remove this argument from the method call; it hides the caller information.
+        _registry = registry;
+    }
 
     private ConcurrentDictionary<string, IsPolicy> ThrowIfNotConcurrentImplementation()
     {

src/Polly/Retry/AsyncRetryPolicy.cs

@@ -21,7 +21,7 @@ internal AsyncRetryPolicy(
         _permittedRetryCount = permittedRetryCount;
         _sleepDurationsEnumerable = sleepDurationsEnumerable;
         _sleepDurationProvider = sleepDurationProvider;
-        _onRetryAsync = onRetryAsync ?? throw new ArgumentNullException(nameof(onRetryAsync));
+        _onRetryAsync = onRetryAsync;
     }
 
     /// <inheritdoc/>
@@ -78,7 +78,7 @@ internal AsyncRetryPolicy(
         _permittedRetryCount = permittedRetryCount;
         _sleepDurationsEnumerable = sleepDurationsEnumerable;
         _sleepDurationProvider = sleepDurationProvider;
-        _onRetryAsync = onRetryAsync ?? throw new ArgumentNullException(nameof(onRetryAsync));
+        _onRetryAsync = onRetryAsync;
     }
 
     /// <inheritdoc/>

src/Polly/Retry/RetryPolicy.cs

@@ -22,7 +22,7 @@ internal RetryPolicy(
         _permittedRetryCount = permittedRetryCount;
         _sleepDurationsEnumerable = sleepDurationsEnumerable;
         _sleepDurationProvider = sleepDurationProvider;
-        _onRetry = onRetry ?? throw new ArgumentNullException(nameof(onRetry));
+        _onRetry = onRetry;
     }
 
     /// <inheritdoc/>
@@ -71,7 +71,7 @@ internal RetryPolicy(
         _permittedRetryCount = permittedRetryCount;
         _sleepDurationsEnumerable = sleepDurationsEnumerable;
         _sleepDurationProvider = sleepDurationProvider;
-        _onRetry = onRetry ?? throw new ArgumentNullException(nameof(onRetry));
+        _onRetry = onRetry;
     }
 
     /// <inheritdoc/>

src/Polly/Timeout/AsyncTimeoutPolicy.cs

@@ -14,9 +14,9 @@ internal AsyncTimeoutPolicy(
         TimeoutStrategy timeoutStrategy,
         Func<Context, TimeSpan, Task, Exception, Task> onTimeoutAsync)
     {
-        _timeoutProvider = timeoutProvider ?? throw new ArgumentNullException(nameof(timeoutProvider));
+        _timeoutProvider = timeoutProvider;
         _timeoutStrategy = timeoutStrategy;
-        _onTimeoutAsync = onTimeoutAsync ?? throw new ArgumentNullException(nameof(onTimeoutAsync));
+        _onTimeoutAsync = onTimeoutAsync;
     }
 
     /// <inheritdoc/>
@@ -58,9 +58,9 @@ internal AsyncTimeoutPolicy(
         TimeoutStrategy timeoutStrategy,
         Func<Context, TimeSpan, Task, Exception, Task> onTimeoutAsync)
     {
-        _timeoutProvider = timeoutProvider ?? throw new ArgumentNullException(nameof(timeoutProvider));
+        _timeoutProvider = timeoutProvider;
         _timeoutStrategy = timeoutStrategy;
-        _onTimeoutAsync = onTimeoutAsync ?? throw new ArgumentNullException(nameof(onTimeoutAsync));
+        _onTimeoutAsync = onTimeoutAsync;
     }
 
     /// <inheritdoc/>

src/Polly/Timeout/AsyncTimeoutSyntax.cs

@@ -418,8 +418,8 @@ public static AsyncTimeoutPolicy TimeoutAsync(
         }
 
         return new AsyncTimeoutPolicy(
-                timeoutProvider,
-                timeoutStrategy,
-                onTimeoutAsync);
+            timeoutProvider,
+            timeoutStrategy,
+            onTimeoutAsync);
     }
 }

src/Polly/Timeout/AsyncTimeoutTResultSyntax.cs

@@ -441,8 +441,8 @@ public static AsyncTimeoutPolicy<TResult> TimeoutAsync<TResult>(Func<Context, Ti
         }
 
         return new AsyncTimeoutPolicy<TResult>(
-                timeoutProvider,
-                timeoutStrategy,
-                onTimeoutAsync);
+            timeoutProvider,
+            timeoutStrategy,
+            onTimeoutAsync);
     }
 }

src/Polly/Timeout/TimeoutPolicy.cs

@@ -14,9 +14,9 @@ internal TimeoutPolicy(
         TimeoutStrategy timeoutStrategy,
         Action<Context, TimeSpan, Task, Exception> onTimeout)
     {
-        _timeoutProvider = timeoutProvider ?? throw new ArgumentNullException(nameof(timeoutProvider));
+        _timeoutProvider = timeoutProvider;
         _timeoutStrategy = timeoutStrategy;
-        _onTimeout = onTimeout ?? throw new ArgumentNullException(nameof(onTimeout));
+        _onTimeout = onTimeout;
     }
 
     /// <inheritdoc/>
@@ -53,9 +53,9 @@ internal TimeoutPolicy(
         TimeoutStrategy timeoutStrategy,
         Action<Context, TimeSpan, Task, Exception> onTimeout)
     {
-        _timeoutProvider = timeoutProvider ?? throw new ArgumentNullException(nameof(timeoutProvider));
+        _timeoutProvider = timeoutProvider;
         _timeoutStrategy = timeoutStrategy;
-        _onTimeout = onTimeout ?? throw new ArgumentNullException(nameof(onTimeout));
+        _onTimeout = onTimeout;
     }
 
     /// <inheritdoc/>

src/Polly/Timeout/TimeoutSyntax.cs

@@ -418,8 +418,8 @@ public static TimeoutPolicy Timeout(
         }
 
         return new TimeoutPolicy(
-                timeoutProvider,
-                timeoutStrategy,
-                onTimeout);
+            timeoutProvider,
+            timeoutStrategy,
+            onTimeout);
     }
 }

src/Polly/Timeout/TimeoutTResultSyntax.cs

@@ -437,8 +437,8 @@ public static TimeoutPolicy<TResult> Timeout<TResult>(
         }
 
         return new TimeoutPolicy<TResult>(
-                timeoutProvider,
-                timeoutStrategy,
-                onTimeout);
+            timeoutProvider,
+            timeoutStrategy,
+            onTimeout);
     }
 }

src/Polly/Utilities/SystemClock.cs

@@ -16,6 +16,7 @@ public static class SystemClock
     public static Action<TimeSpan, CancellationToken> Sleep = (timeSpan, cancellationToken) =>
 #pragma warning restore S2223 // Non-constant static fields should not be visible
     {
+        // Stryker disable once Boolean : no means to test this
         if (cancellationToken.WaitHandle.WaitOne(timeSpan))
         {
             cancellationToken.ThrowIfCancellationRequested();

test/Polly.Specs/Bulkhead/BulkheadSpecs.cs

@@ -94,7 +94,8 @@ public void Should_call_onBulkheadRejected_with_passed_context()
         // Time for the other thread to kick up and take the bulkhead.
         Within(CohesionTimeLimit, () => Expect(0, () => bulkhead.BulkheadAvailableCount, nameof(bulkhead.BulkheadAvailableCount)));
 
-        Should.Throw<BulkheadRejectedException>(() => bulkhead.Execute(_ => { }, contextPassedToExecute));
+        Should.Throw<BulkheadRejectedException>(() => bulkhead.Execute(_ => { }, contextPassedToExecute))
+            .Message.ShouldBe("The bulkhead semaphore and queue are full and execution was rejected.");
 
 #if NET
         tcs.SetCanceled(CancellationToken);

test/Polly.Specs/Caching/AbsoluteTtlSpecs.cs

@@ -32,7 +32,10 @@ public void Should_return_zero_ttl_if_configured_to_expire_in_past()
     {
         AbsoluteTtl ttlStrategy = new AbsoluteTtl(SystemClock.DateTimeOffsetUtcNow().Subtract(TimeSpan.FromTicks(1)));
 
-        ttlStrategy.GetTtl(new Context("someOperationKey"), null).Timespan.ShouldBe(TimeSpan.Zero);
+        var actual = ttlStrategy.GetTtl(new Context("someOperationKey"), null);
+
+        actual.Timespan.ShouldBe(TimeSpan.Zero);
+        actual.SlidingExpiration.ShouldBeFalse();
     }
 
     [Fact]
@@ -44,7 +47,10 @@ public void Should_return_timespan_reflecting_time_until_expiry()
         AbsoluteTtl ttlStrategy = new AbsoluteTtl(tomorrow);
 
         SystemClock.DateTimeOffsetUtcNow = () => today;
-        ttlStrategy.GetTtl(new Context("someOperationKey"), null).Timespan.ShouldBe(TimeSpan.FromDays(1));
+        var actual = ttlStrategy.GetTtl(new Context("someOperationKey"), null);
+
+        actual.Timespan.ShouldBe(TimeSpan.FromDays(1));
+        actual.SlidingExpiration.ShouldBeFalse();
     }
 
     public void Dispose() =>

test/Polly.Specs/Caching/CacheTResultAsyncSpecs.cs

@@ -66,6 +66,14 @@ public void Should_throw_when_ttl_strategy_is_null()
         Should.Throw<ArgumentNullException>(action).ParamName.ShouldBe("ttlStrategy");
     }
 
+    [Fact]
+    public void Should_throw_when_cacheProvider_is_null()
+    {
+        IAsyncCacheProvider nonGenericCacheProvider = null!;
+        Action action = () => nonGenericCacheProvider.AsyncFor<string>();
+        Should.Throw<ArgumentNullException>(action).ParamName.ShouldBe("nonGenericCacheProvider");
+    }
+
     [Fact]
     public void Should_throw_when_cache_key_strategy_is_null()
     {

test/Polly.Specs/Caching/CacheTResultSpecs.cs

@@ -44,6 +44,13 @@ public void Should_throw_when_action_is_null()
             .ParamName.ShouldBe("action");
     }
 
+    [Fact]
+    public void For_throws_if_cache_provider_is_null()
+    {
+        ISyncCacheProvider nonGenericCacheProvider = null!;
+        Should.Throw<ArgumentNullException>(() => nonGenericCacheProvider.For<string>()).ParamName.ShouldBe("nonGenericCacheProvider");
+    }
+
     [Fact]
     public void Should_throw_when_cache_provider_is_null()
     {