add test for DEVSIX-2156

Autoported commit.
Original commit hash: [12da6291f]

Author: Ross Frank

itext.tests/itext.forms.tests/itext/forms/FormFieldFlatteningTest.cs

@@ -41,11 +41,13 @@ source product.
 address: [email protected]
 */
 using System;
+using System.IO;
 using iText.Forms.Fields;
 using iText.Kernel.Colors;
 using iText.Kernel.Pdf;
 using iText.Kernel.Utils;
 using iText.Test;
+using iText.Test.Attributes;
 
 namespace iText.Forms {
     public class FormFieldFlatteningTest : ExtendedITextTest {
@@ -209,5 +211,30 @@ private static void FillTextFieldsThenFlattenThenCompare(String testName) {
             doc.Close();
             NUnit.Framework.Assert.IsNull(new CompareTool().CompareByContent(dest, cmp, destinationFolder, "diff_"));
         }
+
+        /// <exception cref="System.IO.IOException"/>
+        [NUnit.Framework.Test]
+        [LogMessage(iText.IO.LogMessageConstant.DOCUMENT_ALREADY_HAS_FIELD, Count = 3)]
+        public virtual void FlattenReadOnly() {
+            //Logging is expected since there are duplicate field names
+            //isReadOnly should be true after DEVSIX-2156
+            PdfWriter writer = new PdfWriter(new MemoryStream());
+            PdfDocument pdfDoc = new PdfDocument(writer);
+            PdfReader reader = new PdfReader(sourceFolder + "readOnlyForm.pdf");
+            PdfDocument pdfInnerDoc = new PdfDocument(reader);
+            pdfInnerDoc.CopyPagesTo(1, pdfInnerDoc.GetNumberOfPages(), pdfDoc, new PdfPageFormCopier());
+            pdfInnerDoc.Close();
+            reader = new PdfReader(sourceFolder + "readOnlyForm.pdf");
+            pdfInnerDoc = new PdfDocument(reader);
+            pdfInnerDoc.CopyPagesTo(1, pdfInnerDoc.GetNumberOfPages(), pdfDoc, new PdfPageFormCopier());
+            pdfInnerDoc.Close();
+            PdfAcroForm form = PdfAcroForm.GetAcroForm(pdfDoc, false);
+            bool isReadOnly = true;
+            foreach (PdfFormField field in form.GetFormFields().Values) {
+                isReadOnly = (isReadOnly && field.IsReadOnly());
+            }
+            pdfDoc.Close();
+            NUnit.Framework.Assert.IsFalse(isReadOnly);
+        }
     }
 }

itext.tests/itext.forms.tests/resources/itext/forms/FormFieldFlatteningTest/readOnlyForm.pdf

@@ -1 +1 @@
-b7a901674e5cb6ae3c018047fdc5c80598478de2
+12da6291f4df3a21df2574d7028b68353bc5a912