diff --git a/modules/ingest-common/src/test/java/org/elasticsearch/ingest/common/RegisteredDomainProcessorTests.java b/modules/ingest-common/src/test/java/org/elasticsearch/ingest/common/RegisteredDomainProcessorTests.java
index f63aff0518072..f9d35b902c9d8 100644
--- a/modules/ingest-common/src/test/java/org/elasticsearch/ingest/common/RegisteredDomainProcessorTests.java
+++ b/modules/ingest-common/src/test/java/org/elasticsearch/ingest/common/RegisteredDomainProcessorTests.java
@@ -17,6 +17,13 @@
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 
+/**
+ * Test parsing of an eTLD from a FQDN. The list of eTLDs is maintained here:
+ *   https://github.com/publicsuffix/list/blob/master/public_suffix_list.dat
+ *
+ * Effective TLDs (eTLS) are not the same as DNS TLDs. Uses for eTLDs are listed here.
+ *   https://publicsuffix.org/learn/
+ */
 public class RegisteredDomainProcessorTests extends ESTestCase {
     private Map<String, Object> buildEvent(String domain) {
         return new HashMap<>() {
@@ -33,6 +40,21 @@ public void testBasic() throws Exception {
         testRegisteredDomainProcessor(buildEvent("."), null, null, null, null);
         testRegisteredDomainProcessor(buildEvent("$"), null, null, null, null);
         testRegisteredDomainProcessor(buildEvent("foo.bar.baz"), null, null, null, null);
+        testRegisteredDomainProcessor(buildEvent("www.books.amazon.co.uk"), "www.books.amazon.co.uk", "amazon.co.uk", "co.uk", "www.books");
+        // Verify "com" is returned as the eTLD, for that FQDN or subdomain
+        testRegisteredDomainProcessor(buildEvent("com"), "com", null, "com", null);
+        testRegisteredDomainProcessor(buildEvent("example.com"), "example.com", "example.com", "com", null);
+        // Verify "googleapis.com" is returned as the eTLD, for that FQDN or subdomain
+        testRegisteredDomainProcessor(buildEvent("googleapis.com"), "googleapis.com", null, "googleapis.com", null);
+        testRegisteredDomainProcessor(
+            buildEvent("content-autofill.googleapis.com"),
+            "content-autofill.googleapis.com",
+            "content-autofill.googleapis.com",
+            "googleapis.com",
+            null
+        );
+        // Verify "global.ssl.fastly.net" is returned as the eTLD, for that FQDN or subdomain
+        testRegisteredDomainProcessor(buildEvent("global.ssl.fastly.net"), "global.ssl.fastly.net", null, "global.ssl.fastly.net", null);
         testRegisteredDomainProcessor(
             buildEvent("1.www.global.ssl.fastly.net"),
             "1.www.global.ssl.fastly.net",
@@ -40,7 +62,6 @@ public void testBasic() throws Exception {
             "global.ssl.fastly.net",
             "1"
         );
-        testRegisteredDomainProcessor(buildEvent("www.books.amazon.co.uk"), "www.books.amazon.co.uk", "amazon.co.uk", "co.uk", "www.books");
     }
 
     public void testUseRoot() throws Exception {