Return some more useful info on test failure

Author: nblumhardt

test/Serilog.Sinks.File.Tests/RollingFileSinkTests.cs

@@ -88,9 +88,9 @@ public void WhenSizeLimitIsBreachedNewFilesCreated()
                 var files = Directory.GetFiles(temp.Path).OrderBy(p => p).ToArray();
 
                 Assert.Equal(3, files.Length);
-                Assert.False(files[0].Contains("_000.txt"));
-                Assert.True(files[1].Contains("_001.txt"));
-                Assert.True(files[2].Contains("_002.txt"));
+                Assert.False(files[0].Contains("_000.txt"), files[0]);
+                Assert.True(files[1].Contains("_001.txt"), files[1]);
+                Assert.True(files[2].Contains("_002.txt"), files[2]);
             }
         }