Improve LogAnalysis tests (#1696)

I noticed that a lot of the community solutions to the SubstringBetween where simply accidentally correct, doing

    s.Substring(s.IndexOf(first) + first.Length, s.IndexOf(last) - last.Length);

i.e. thinking that the length of the last delimiter is relevant, which looks symmetrical to the handling of the first Substring parameter, and just happens to be correct on the provided string.

Author: marhel

exercises/concept/log-analysis/LogAnalysisTests.cs

@@ -22,6 +22,12 @@ public void SubstringBetween()
         Assert.Equal("INFO", "[INFO]: File Deleted.".SubstringBetween("[", "]"));
     }
 
+    [Fact(Skip = "Remove this Skip property to run this test")]
+    public void SubstringBetweenLongerDelimiters()
+    {
+        Assert.Equal("SOMETHING", "FIND >>> SOMETHING <===< HERE".SubstringBetween(">>> ", " <===<"));
+    }
+    
     [Fact(Skip = "Remove this Skip property to run this test")]
     public void Message()
     {