Add red tests reproducing #4839

Author: Vogel612

RubberduckTests/RegexAssistant/CharacterClassTests.cs

@@ -210,5 +210,25 @@ public void IgnoresBackreferenceSpecifiers()
                 Assert.AreEqual(expectedSpecifiers[i], cut.CharacterSpecifiers[i]);
             }
         }
+
+        [Test]
+        // https://github.com/rubberduck-vba/Rubberduck/issues/4839
+        public void TrailingEscapedBackslash()
+        {
+            const string pattern = @"[^\w\\]";
+
+            var expression = VBRegexParser.Parse(pattern);
+            Assert.IsInstanceOf(typeof(SingleAtomExpression), expression);
+            var atom = (expression as SingleAtomExpression).Atom;
+            Assert.AreEqual(new CharacterClass(@"[^\w\\]", Quantifier.None), atom);
+        }
+
+        [Test]
+        // https://github.com/rubberduck-vba/Rubberduck/issues/4839
+        public void TrailingEscapedBackslashIsConstructible()
+        {
+            const string pattern = @"[^\w\\]";
+            new CharacterClass(pattern, Quantifier.None);
+        }
     }
 }