[SPARK-16598][SQL][TEST] Added a test case for verifying the table identifier parsing

#### What changes were proposed in this pull request?
So far, the test cases of `TableIdentifierParserSuite` do not cover the quoted cases. We should add one for avoiding regression.

#### How was this patch tested?
N/A

Author: gatorsmile <gatorsmile@gmail.com>

Closes #14244 from gatorsmile/quotedIdentifiers.

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/TableIdentifierParserSuite.scala

@@ -68,6 +68,14 @@ class TableIdentifierParserSuite extends SparkFunSuite {
     }
   }
 
+  test("quoted identifiers") {
+    assert(TableIdentifier("z", Some("x.y")) === parseTableIdentifier("`x.y`.z"))
+    assert(TableIdentifier("y.z", Some("x")) === parseTableIdentifier("x.`y.z`"))
+    assert(TableIdentifier("z", Some("`x.y`")) === parseTableIdentifier("```x.y```.z"))
+    assert(TableIdentifier("`y.z`", Some("x")) === parseTableIdentifier("x.```y.z```"))
+    assert(TableIdentifier("x.y.z", None) === parseTableIdentifier("`x.y.z`"))
+  }
+
   test("table identifier - strict keywords") {
     // SQL Keywords.
     hiveStrictNonReservedKeyword.foreach { keyword =>