Fix coverage holes.

Author: sharpjs

DependencyQueue.Tests/DependencyQueueTests.cs

@@ -146,6 +146,18 @@ public void Enqueue_EmptyInRequires()
         e.ParamName.ShouldBe("requires");
     }
 
+    [Test]
+    public void Enqueue_NullEntry()
+    {
+        using var queue = new Queue();
+
+        var e = Should.Throw<ArgumentNullException>(
+            () => queue.Enqueue(null!)
+        );
+
+        e.ParamName.ShouldBe("entry");
+    }
+
     [Test]
     public void Enqueue_IndependentEntry()
     {

DependencyQueue/Errors.cs

@@ -17,9 +17,6 @@ internal static Exception ArgumentContainsNull(string name)
     internal static Exception ArgumentContainsEmpty(string name)
         => new ArgumentException("Argument cannot contain an empty item.", name);
 
-    internal static Exception ArgumentOutOfRange(string name)
-        => new ArgumentOutOfRangeException(name);
-
     internal static Exception ObjectDisposed(string? name)
         => new ObjectDisposedException(name);