Test: Fix flaky DocumentTests by using arrays

Tests/DocumentTests/Utils.cs

@@ -1,5 +1,6 @@
 using Elwig.Documents;
 using NReco.PdfRenderer;
+using System.Text.RegularExpressions;
 
 namespace Tests.DocumentTests {
     public static class Utils {
@@ -16,5 +17,13 @@ namespace Tests.DocumentTests {
                 File.Delete(FileName);
             }
         }
+
+        public static string[][] ExtractTable(string text) {
+            return text.Split('\n')
+                .Select(row => Regex.Split(row, @"\s{2,}").Select(c => c.Trim()).ToArray())
+                .Where(row => row.Length > 3)
+                .Skip(1)
+                .ToArray();
+        }
     }
 }