check public api through reflection

src/UglyToad.Pdf.Tests/PublicApiScannerTests.cs

@@ -0,0 +1,43 @@
+namespace UglyToad.Pdf.Tests
+{
+    using System.Collections.Generic;
+    using System.Linq;
+    using Xunit;
+
+    public class PublicApiScannerTests
+    {
+        [Fact]
+        public void OnlyExposedApiIsPublic()
+        {
+            var assembly = typeof(PdfDocument).Assembly;
+
+            var types = assembly.GetTypes();
+
+            var publicTypeNames = new List<string>();
+
+            foreach (var type in types)
+            {
+                if (type.IsPublic)
+                {
+                    publicTypeNames.Add(type.FullName);
+                }
+            }
+
+            var expected = new List<string>
+            {
+                "UglyToad.Pdf.PdfDocument",
+                "UglyToad.Pdf.ParsingOptions",
+                "UglyToad.Pdf.Logging.ILog",
+                "UglyToad.Pdf.Geometry.PdfPoint",
+                "UglyToad.Pdf.Fonts.Exceptions.InvalidFontFormatException",
+                "UglyToad.Pdf.Exceptions.PdfDocumentFormatException",
+                "UglyToad.Pdf.Content.Letter",
+                "UglyToad.Pdf.Content.Page",
+                "UglyToad.Pdf.Content.PageSize",
+                "UglyToad.Pdf.Content.DocumentInformation"
+            };
+
+            Assert.Equal(expected.OrderBy(x => x), publicTypeNames.OrderBy(x => x));
+        }
+    }
+}

src/UglyToad.Pdf/Filters/IPngPredictor.cs

@@ -0,0 +1,7 @@
+namespace UglyToad.Pdf.Filters
+{
+    internal interface IPngPredictor
+    {
+        byte[] Decode(byte[] input, int predictor, int colors, int bitsPerComponent, int columns);
+    }
+}

src/UglyToad.Pdf/Filters/PngPredictor.cs

@@ -231,9 +231,4 @@
             return (by & mask) | (truncatedVal << startBit);
         }
     }
-
-    public interface IPngPredictor
-    {
-        byte[] Decode(byte[] input, int predictor, int colors, int bitsPerComponent, int columns);
-    }
 }

src/UglyToad.Pdf/Util/Hex.cs

@@ -7,7 +7,7 @@
      *
      * @author John Hewson
      */
-    public class Hex
+    internal class Hex
     {
         /**
          * for hex conversion.