diff --git a/core/fxge/dib/cfx_dibitmap_unittest.cpp b/core/fxge/dib/cfx_dibitmap_unittest.cpp
index 67ca705..8563bf9 100644
--- a/core/fxge/dib/cfx_dibitmap_unittest.cpp
+++ b/core/fxge/dib/cfx_dibitmap_unittest.cpp
@@ -13,3 +13,84 @@
   pBitmap = pdfium::MakeRetain<CFX_DIBitmap>();
   EXPECT_TRUE(pBitmap->Create(400, 300, FXDIB_1bppRgb));
 }
+
+TEST(CFX_DIBitmap, CalculatePitchAndSizeGood) {
+  // Simple case with no provided pitch.
+  Optional<CFX_DIBitmap::PitchAndSize> result =
+      CFX_DIBitmap::CalculatePitchAndSize(100, 200, FXDIB_Argb, 0);
+  ASSERT_TRUE(result.has_value());
+  EXPECT_EQ(400u, result.value().pitch);
+  EXPECT_EQ(80000u, result.value().size);
+
+  // Simple case with no provided pitch and different format.
+  result = CFX_DIBitmap::CalculatePitchAndSize(100, 200, FXDIB_8bppRgb, 0);
+  ASSERT_TRUE(result.has_value());
+  EXPECT_EQ(100u, result.value().pitch);
+  EXPECT_EQ(20000u, result.value().size);
+
+  // Simple case with provided pitch.
+  result = CFX_DIBitmap::CalculatePitchAndSize(100, 200, FXDIB_Argb, 400);
+  ASSERT_TRUE(result.has_value());
+  EXPECT_EQ(400u, result.value().pitch);
+  EXPECT_EQ(80000u, result.value().size);
+
+  // Simple case with provided pitch, but pitch does not match width * bpp.
+  result = CFX_DIBitmap::CalculatePitchAndSize(100, 200, FXDIB_Argb, 355);
+  ASSERT_TRUE(result.has_value());
+  EXPECT_EQ(355u, result.value().pitch);
+  EXPECT_EQ(71000u, result.value().size);
+}
+
+TEST(CFX_DIBitmap, CalculatePitchAndSizeBad) {
+  // Bad width / height.
+  static const CFX_Size kBadDimensions[] = {
+      {0, 0},   {-1, -1}, {-1, 0},   {0, -1},
+      {0, 200}, {100, 0}, {-1, 200}, {100, -1},
+  };
+  for (const auto& dimension : kBadDimensions) {
+    EXPECT_FALSE(CFX_DIBitmap::CalculatePitchAndSize(
+        dimension.width, dimension.height, FXDIB_Argb, 0));
+    EXPECT_FALSE(CFX_DIBitmap::CalculatePitchAndSize(
+        dimension.width, dimension.height, FXDIB_Argb, 1));
+  }
+
+  // Bad format.
+  EXPECT_FALSE(CFX_DIBitmap::CalculatePitchAndSize(100, 200, FXDIB_Invalid, 0));
+  EXPECT_FALSE(
+      CFX_DIBitmap::CalculatePitchAndSize(100, 200, FXDIB_Invalid, 800));
+
+  // Overflow cases with calculated pitch.
+  EXPECT_FALSE(
+      CFX_DIBitmap::CalculatePitchAndSize(1073747000, 1, FXDIB_Argb, 0));
+  EXPECT_FALSE(
+      CFX_DIBitmap::CalculatePitchAndSize(1048576, 1024, FXDIB_Argb, 0));
+  EXPECT_FALSE(
+      CFX_DIBitmap::CalculatePitchAndSize(4194304, 1024, FXDIB_8bppRgb, 0));
+
+  // Overflow cases with provided pitch.
+  EXPECT_FALSE(CFX_DIBitmap::CalculatePitchAndSize(1073741824, 1, FXDIB_Argb,
+                                                   1073741824));
+  EXPECT_FALSE(
+      CFX_DIBitmap::CalculatePitchAndSize(1048576, 1024, FXDIB_Argb, 4194304));
+  EXPECT_FALSE(CFX_DIBitmap::CalculatePitchAndSize(4194304, 1024, FXDIB_8bppRgb,
+                                                   4194304));
+}
+
+TEST(CFX_DIBitmap, CalculatePitchAndSizeBoundary) {
+  // Test boundary condition for pitch overflow.
+  Optional<CFX_DIBitmap::PitchAndSize> result =
+      CFX_DIBitmap::CalculatePitchAndSize(268435452, 4, FXDIB_8bppRgb, 0);
+  ASSERT_TRUE(result);
+  EXPECT_EQ(268435452u, result.value().pitch);
+  EXPECT_EQ(1073741808u, result.value().size);
+  EXPECT_FALSE(
+      CFX_DIBitmap::CalculatePitchAndSize(268435453, 4, FXDIB_8bppRgb, 0));
+
+  // Test boundary condition for size overflow.
+  result = CFX_DIBitmap::CalculatePitchAndSize(17043520, 63, FXDIB_8bppRgb, 0);
+  ASSERT_TRUE(result);
+  EXPECT_EQ(17043520u, result.value().pitch);
+  EXPECT_EQ(1073741760u, result.value().size);
+  EXPECT_FALSE(
+      CFX_DIBitmap::CalculatePitchAndSize(17043521, 63, FXDIB_8bppRgb, 0));
+}