Test zero-width chars nested within false delimiter

Author: maustinstar

test/Parse/raw_string.swift

@@ -68,8 +68,14 @@ _ = ##"""
       """##
 // CHECK: "a raw string with \"\"\" in it"
 
-_ = #"""#
-// CHECK: "\""
+// ===---------- False Multiline Delimiters --------===
+
+/// Source code contains zero-width character in this format `#"[U+200B]"[U+200B]"#`
+/// The check contains the zero-width character in this format: `"[U+200B]\"[U+200B]"`
+/// Use this test when implementating `diagnoseZeroWidthMatchAndAdvance`.
+/// See https://bugs.swift.org/browse/SR-8678
+_ = #"​"​"#
+// CHECK: "​\"​"
 
 _ = #""""#
 // CHECK: "\"\""
@@ -80,6 +86,9 @@ _ = #"""""#
 _ = #""""""#
 // CHECK: "\"\"\"\""
 
+_ = #"""#
+// CHECK: "\""
+
 _ = ##""" foo # "# "##
 // CHECK: "\"\" foo # \"# "