diff --git a/unitTests/test_pngimage.cpp b/unitTests/test_pngimage.cpp
index 82fec574..ccdbb893 100644
--- a/unitTests/test_pngimage.cpp
+++ b/unitTests/test_pngimage.cpp
@@ -24,16 +24,18 @@
 
 #include <array>
 #include <algorithm>
+#include <memory>
+#include <sstream>
 
 using namespace Exiv2;
 
 TEST(PngChunk, keyTxtChunkExtractsKeywordCorrectlyInPresenceOfNullChar)
 {
   // The following data is: '\0\0"AzTXtRaw profile type exif\0\0x'
-  std::array<std::uint8_t, 32> data{0x00, 0x00, 0x22, 0x41, 0x7a, 0x54, 0x58, 0x74,
-                                    0x52, 0x61, 0x77, 0x20, 0x70, 0x72, 0x6f, 0x66,
-                                    0x69, 0x6c, 0x65, 0x20, 0x74, 0x79, 0x70, 0x65,
-                                    0x20, 0x65, 0x78, 0x69, 0x66, 0x00, 0x00, 0x78};
+  const std::array<std::uint8_t, 32> data{0x00, 0x00, 0x22, 0x41, 0x7a, 0x54, 0x58, 0x74,
+                                          0x52, 0x61, 0x77, 0x20, 0x70, 0x72, 0x6f, 0x66,
+                                          0x69, 0x6c, 0x65, 0x20, 0x74, 0x79, 0x70, 0x65,
+                                          0x20, 0x65, 0x78, 0x69, 0x66, 0x00, 0x00, 0x78};
 
   DataBuf chunkBuf(data.data(), static_cast<long>(data.size()));
   DataBuf key = Internal::PngChunk::keyTXTChunk(chunkBuf, true);
@@ -46,11 +48,167 @@ TEST(PngChunk, keyTxtChunkExtractsKeywordCorrectlyInPresenceOfNullChar)
 TEST(PngChunk, keyTxtChunkThrowsExceptionWhenThereIsNoNullChar)
 {
   // The following data is: '\0\0"AzTXtRaw profile type exifx'
-  std::array<std::uint8_t, 30> data{0x00, 0x00, 0x22, 0x41, 0x7a, 0x54, 0x58, 0x74,
-                                    0x52, 0x61, 0x77, 0x20, 0x70, 0x72, 0x6f, 0x66,
-                                    0x69, 0x6c, 0x65, 0x20, 0x74, 0x79, 0x70, 0x65,
-                                    0x20, 0x65, 0x78, 0x69, 0x66, 0x78};
+  const std::array<std::uint8_t, 30> data{0x00, 0x00, 0x22, 0x41, 0x7a, 0x54, 0x58, 0x74,
+                                          0x52, 0x61, 0x77, 0x20, 0x70, 0x72, 0x6f, 0x66,
+                                          0x69, 0x6c, 0x65, 0x20, 0x74, 0x79, 0x70, 0x65,
+                                          0x20, 0x65, 0x78, 0x69, 0x66, 0x78};
 
   DataBuf chunkBuf(data.data(), static_cast<long>(data.size()));
   ASSERT_THROW(Internal::PngChunk::keyTXTChunk(chunkBuf, true), Exiv2::Error);
 }
+
+TEST(PngChunk, keyTxtChunkThrowsIfSizeIsNotEnough)
+{
+  const std::array<std::uint8_t, 4> data{0x00, 0x00, 0x22, 0x41};
+  DataBuf chunkBuf(data.data(), static_cast<long>(data.size()));
+  ASSERT_THROW(Internal::PngChunk::keyTXTChunk(chunkBuf, true), Exiv2::Error);
+
+  DataBuf emptyChunk(data.data(), 0);
+  ASSERT_THROW(Internal::PngChunk::keyTXTChunk(emptyChunk, false), Exiv2::Error);
+}
+
+
+TEST(PngImage, canBeCreatedFromScratch)
+{
+    auto memIo = std::make_unique<MemIo>();
+    const bool create {true};
+    ASSERT_NO_THROW(PngImage png(std::move(memIo), create));
+}
+
+TEST(PngImage, canBeOpenedEvenWithAnEmptyMemIo)
+{
+    auto memIo = std::make_unique<MemIo>();
+    const bool create {false};
+    ASSERT_NO_THROW(PngImage png(std::move(memIo), create));
+}
+
+TEST(PngImage, mimeTypeIsPng)
+{
+    auto memIo = std::make_unique<MemIo>();
+    const bool create {true};
+    PngImage png(std::move(memIo), create);
+
+    ASSERT_EQ("image/png", png.mimeType());
+}
+
+TEST(PngImage, printStructurePrintsNothingWithKpsNone)
+{
+    auto memIo = std::make_unique<MemIo>();
+    const bool create {true};
+    PngImage png(std::move(memIo), create);
+
+    std::ostringstream stream;
+    png.printStructure(stream, Exiv2::kpsNone, 1);
+
+    ASSERT_TRUE(stream.str().empty());
+}
+
+TEST(PngImage, printStructurePrintsDataWithKpsBasic)
+{
+    auto memIo = std::make_unique<MemIo>();
+    const bool create {true};
+    PngImage png(std::move(memIo), create);
+
+    std::ostringstream stream;
+    png.printStructure(stream, Exiv2::kpsBasic, 1);
+
+    ASSERT_FALSE(stream.str().empty());
+}
+
+TEST(PngImage, cannotReadMetadataFromEmptyIo)
+{
+    auto memIo = std::make_unique<MemIo>();
+    const bool create {false};
+    PngImage png(std::move(memIo), create);
+
+    try {
+      png.readMetadata();
+      FAIL();
+    }  catch (const Exiv2::Error& e) {
+      ASSERT_EQ(kerNotAnImage, e.code());
+      ASSERT_STREQ("This does not look like a PNG image", e.what());
+    }
+}
+
+TEST(PngImage, cannotReadMetadataFromIoWhichCannotBeOpened)
+{
+    auto memIo = std::make_unique<FileIo>("NonExistingPath.png");
+    const bool create {false};
+    PngImage png(std::move(memIo), create);
+
+    try {
+      png.readMetadata();
+      FAIL();
+    }  catch (const Exiv2::Error& e) {
+      ASSERT_EQ(kerDataSourceOpenFailed, e.code());
+    }
+}
+
+TEST(PngImage, cannotWriteMetadataToEmptyIo)
+{
+    auto memIo = std::make_unique<MemIo>();
+    const bool create {false};
+    PngImage png(std::move(memIo), create);
+
+    try {
+      png.writeMetadata();
+      FAIL();
+    }  catch (const Exiv2::Error& e) {
+      ASSERT_EQ(kerNoImageInInputData, e.code());
+    }
+}
+
+TEST(PngImage, cannotWriteMetadataToIoWhichCannotBeOpened)
+{
+    auto memIo = std::make_unique<FileIo>("NonExistingPath.png");
+    const bool create {false};
+    PngImage png(std::move(memIo), create);
+
+    try {
+      png.readMetadata();
+      FAIL();
+    }  catch (const Exiv2::Error& e) {
+      ASSERT_EQ(kerDataSourceOpenFailed, e.code());
+    }
+}
+
+
+TEST(isPngType, withValidSignatureReturnsTrue)
+{
+    const unsigned char pngSignature[8] = { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A };
+    MemIo memIo(pngSignature, 8);
+    ASSERT_TRUE(isPngType(memIo, false));
+}
+
+TEST(isPngType, withInvalidSignatureReturnsFalse)
+{
+    const unsigned char pngSignature[8] = { 0x69, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A };
+    MemIo memIo(pngSignature, 8);
+    ASSERT_FALSE(isPngType(memIo, false));
+}
+
+TEST(isPngType, withShorterDataReturnsFalse)
+{
+    const unsigned char pngSignature[6] = { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A};
+    MemIo memIo(pngSignature, 6);
+    ASSERT_FALSE(isPngType(memIo, false));
+}
+
+TEST(isPngType, withEmptyDataReturnsFalse)
+{
+    MemIo memIo;
+    ASSERT_FALSE(isPngType(memIo, false));
+}
+
+TEST(isPngType, withMemIoInErroneousStatusThrows)
+{
+    MemIo memIo;
+    memIo.getb();
+
+    try {
+      isPngType(memIo, false);
+      FAIL();
+    }  catch (const Exiv2::Error& e) {
+      ASSERT_EQ(kerInputDataReadFailed, e.code());
+    }
+}