Add an ImportRuleCssSourceTest class

Author: W Hörchner

PreMailer.Net/PreMailer.Net.Tests/ImportRuleCssSourceTests.cs

@@ -0,0 +1,48 @@
+using AngleSharp.Html.Parser;
+using Xunit;
+using Moq;
+using PreMailer.Net.Downloaders;
+using PreMailer.Net.Sources;
+using System;
+using System.Text;
+using System.IO;
+using System.Collections.Generic;
+
+
+namespace PreMailer.Net.Tests
+{
+	public class ImportRuleCssSourceTests
+	{
+		private readonly Mock<IWebDownloader> _webDownloader = new Mock<IWebDownloader>();
+
+
+		[Fact]
+		public void FetchImportRules()
+		{
+			var baseUri = new Uri("https://a.com");
+			var urls = new List<string>() { "variables.css", "/fonts.css", "https://fonts.google.com/css/test-font" };
+
+			var css = CreateCss(urls);
+			var contents = ImportRuleCssSource.FetchImportRules(baseUri, css);
+
+			foreach (var url in urls)
+			{
+				_webDownloader.Verify(w => w.DownloadString(It.Is<Uri>(u => u.Equals(new Uri(baseUri, url)))));
+			}
+
+		}
+
+		private string CreateCss(IEnumerable<string> imports)
+		{
+			WebDownloader.SharedDownloader = _webDownloader.Object;
+
+			var builder = new StringBuilder();
+			foreach (var import in imports)
+			{
+				builder.AppendLine($"@import \"{import}\";");
+			}
+
+			return builder.ToString();
+		}
+	}
+}

PreMailer.Net/PreMailer.Net/Sources/ImportRuleCssSource.cs

@@ -71,7 +71,7 @@ private void DownloadContents()
 				throw new WebException($"PreMailer.Net is unable to download the requested URL: {_downloadUri}", ex);
 			}
 
-			if (_level < 2) // Stop processing imports at level 2
+			if (_level < 2 && cssContents != null) // Stop processing imports at level 2
 			{
 				FetchImportRules(_downloadUri, cssContents, _level + 1, _contentBuilder, _importList);
 			}
@@ -94,6 +94,11 @@ private static bool IsSupported(string scheme)
 		/// <returns></returns>
 		public static string FetchImportRules(Uri downloadUri, string contents)
 		{
+			if (contents == null)
+			{
+				return string.Empty;
+			}
+
 			var contentBuilder = new StringBuilder();
 			var importList = new List<Uri>();
 
@@ -123,6 +128,7 @@ public static string FetchImportRules(Uri downloadUri, string contents)
 		/// <param name="importList"></param>
 		private static void FetchImportRules(Uri downloadUri, string contents, int level, StringBuilder contentBuilder, List<Uri> importList)
 		{
+
 			string indent = level > 0 ? new string('\t', level) : string.Empty;
 			int cnt = 0;