Test for adding image with transparent background

SpreadCheetah.Test/Tests/SpreadsheetImageTests.cs

@@ -186,6 +186,37 @@ public async Task Spreadsheet_AddImage_Png()
         Assert.Equal("Image 1", picture.Name);
     }
 
+    [Fact]
+    public async Task Spreadsheet_AddImage_PngWithTransparentBackground()
+    {
+        // Arrange
+        const string reference = "B3";
+        using var pngStream = EmbeddedResources.GetStream("yellow-500x500-transparent.png");
+        using var outputStream = new MemoryStream();
+        await using var spreadsheet = await Spreadsheet.CreateNewAsync(outputStream);
+        var embeddedImage = await spreadsheet.EmbedImageAsync(pngStream);
+        await spreadsheet.StartWorksheetAsync("Sheet 1");
+        var canvas = ImageCanvas.OriginalSize(reference.AsSpan());
+
+        // Act
+        spreadsheet.AddImage(canvas, embeddedImage);
+
+        // Assert
+        await spreadsheet.FinishAsync();
+        SpreadsheetAssert.Valid(outputStream);
+
+        using var workbook = new XLWorkbook(outputStream);
+        var worksheet = Assert.Single(workbook.Worksheets);
+        var picture = Assert.Single(worksheet.Pictures);
+        Assert.Equal(reference, picture.TopLeftCell.Address.ToString());
+        Assert.Equal(XLPictureFormat.Png, picture.Format);
+        Assert.Equal(500, picture.OriginalWidth);
+        Assert.Equal(500, picture.OriginalHeight);
+        Assert.Equal(0, picture.Top);
+        Assert.Equal(0, picture.Left);
+        Assert.Equal("Image 1", picture.Name);
+    }
+
     [Fact]
     public async Task Spreadsheet_AddImage_PngWithLargeResolution()
     {
@@ -690,6 +721,4 @@ public async Task Spreadsheet_AddImage_PngWithFillCellsAndOffsets(int left, int
         Assert.Equal(expectedWidth, actualWidth);
         Assert.Equal(expectedHeight, actualHeight);
     }
-
-    // TODO: Test for transparent image
 }