add tests for IsEncryptedOfficeFile and GetTestFilePath method

Author: mikeebowen

test/DocumentFormat.OpenXml.Packaging.Tests/OpenXmlPackageTests.cs

@@ -342,5 +342,55 @@ public void SucceedWithMissingCalcChainPart()
 
             Assert.NotNull(spd);
         }
+
+        [Fact]
+        public void IsEncryptedOfficeFile_ReturnsTrue_ForEncryptedFile()
+        {
+            using (Stream stream = GetStream(TestFiles.Encrypted_pptx, false))
+            {
+                Assert.True(OpenXmlPackage.IsEncryptedOfficeFile(stream));
+            }
+        }
+
+        [Fact]
+        public void IsEncryptedOfficeFile_ReturnsFalse_ForUnencryptedFile()
+        {
+            using (Stream stream = GetStream(TestFiles.Presentation, false))
+            {
+                Assert.False(OpenXmlPackage.IsEncryptedOfficeFile(stream));
+            }
+        }
+
+        [Fact]
+        public void IsEncryptedOfficeFile_ThrowsArgumentNullException_ForNullStream()
+        {
+            Assert.Throws<ArgumentNullException>(() => OpenXmlPackage.IsEncryptedOfficeFile((Stream)null!));
+        }
+
+        [Fact]
+        public void IsEncryptedOfficeFile_ThrowsArgumentException_ForUnseekableStream()
+        {
+            var unseekable = new UnseekableStream();
+            Assert.Throws<ArgumentException>(() => OpenXmlPackage.IsEncryptedOfficeFile(unseekable));
+        }
+
+        private class UnseekableStream : MemoryStream
+        {
+            public override bool CanSeek => false;
+        }
+
+        [Fact]
+        public void IsEncryptedOfficeFile_ReturnsTrue_ForEncryptedFilePath()
+        {
+            string filePath = GetTestFilePath(TestFiles.Encrypted_pptx);
+            Assert.True(OpenXmlPackage.IsEncryptedOfficeFile(filePath));
+        }
+
+        [Fact]
+        public void IsEncryptedOfficeFile_ReturnsFalse_ForUnencryptedFile_FromString()
+        {
+            string filePath = GetTestFilePath(TestFiles.Presentation);
+            Assert.False(OpenXmlPackage.IsEncryptedOfficeFile(filePath));
+        }
     }
 }

test/DocumentFormat.OpenXml.Tests.Assets/TestAssets.cs

@@ -71,6 +71,26 @@ public static Stream GetStream(string name, bool isEditable)
             return isEditable ? stream.AsMemoryStream() : stream;
         }
 
+        /// <summary>
+        /// Extracts an embedded test resource to a temporary file and returns its file path.
+        /// </summary>
+        /// <param name="resourceName">The name of the embedded resource to extract.</param>
+        /// <returns>The full path to the temporary file containing the resource data.</returns>
+        /// <remarks>
+        /// The caller is responsible for deleting the temporary file after use.
+        /// </remarks>
+        public static string GetTestFilePath(string resourceName)
+        {
+            string tempPath = Path.Combine(Path.GetTempPath(), Guid.NewGuid() + Path.GetExtension(resourceName));
+
+            using (Stream stream = GetStream(resourceName, false))
+            using (FileStream fileStream = File.Create(tempPath))
+            {
+                stream.CopyTo(fileStream);
+                return tempPath;
+            }
+        }
+
         private static Stream AsMemoryStream(this Stream stream)
         {
             if (stream is MemoryStream ms)