Add test. DEVSIX-2187

Autoported commit.
Original commit hash: [5b04a612e]

Author: JonPReilly

itext.tests/itext.forms.tests/itext/forms/PdfFormCopyTest.cs

@@ -168,6 +168,31 @@ public virtual void CopyFieldsTest05() {
                 , destinationFolder, "diff_"));
         }
 
+        /// <exception cref="System.IO.IOException"/>
+        /// <exception cref="System.Exception"/>
+        [NUnit.Framework.Test]
+        [LogMessage(iText.IO.LogMessageConstant.DOCUMENT_ALREADY_HAS_FIELD, Count = 2)]
+        public virtual void CopyMultipleSubfieldsTest01() {
+            String srcFilename = sourceFolder + "copyMultipleSubfieldsTest01.pdf";
+            String destFilename = destinationFolder + "copyMultipleSubfieldsTest01.pdf";
+            PdfDocument srcDoc = new PdfDocument(new PdfReader(srcFilename));
+            PdfDocument destDoc = new PdfDocument(new PdfWriter(destFilename));
+            PdfPageFormCopier pdfPageFormCopier = new PdfPageFormCopier();
+            // copying the same page from the same document twice
+            for (int i = 0; i < 2; ++i) {
+                srcDoc.CopyPagesTo(1, 1, destDoc, pdfPageFormCopier);
+            }
+            PdfAcroForm acroForm = PdfAcroForm.GetAcroForm(destDoc, false);
+            acroForm.GetField("text_1").SetValue("Text 1!");
+            acroForm.GetField("text_2").SetValue("Text 2!");
+            acroForm.GetField("text.3").SetValue("Text 3!");
+            acroForm.GetField("text.4").SetValue("Text 4!");
+            destDoc.Close();
+            srcDoc.Close();
+            NUnit.Framework.Assert.IsNull(new CompareTool().CompareByContent(destFilename, sourceFolder + "cmp_copyMultipleSubfieldsTest01.pdf"
+                , destinationFolder, "diff_"));
+        }
+
         /// <exception cref="System.IO.IOException"/>
         /// <exception cref="System.Exception"/>
         [NUnit.Framework.Test]

itext.tests/itext.forms.tests/resources/itext/forms/PdfFormFieldsCopyTest/cmp_copyMultipleSubfieldsTest01.pdf

@@ -1 +1 @@
-c8dc9feec441f2ed9b46c8a5c3b75978eb017f6b
+5b04a612e5541d864c1d8bbc4932176e39ece268