Adding test for invalid and inexistent DNS domains

tests/test_wakunode.nim

@@ -240,6 +240,40 @@ suite "WakuNode":
       not ipStr.contains("0.0.0.0")
       not ipStr.contains("127.0.0.1")
 
+  asyncTest "Node creation fails when invalid dns4 address is provided":
+    let
+      nodeKey = generateSecp256k1Key()
+      bindIp = ValidIpAddress.init("0.0.0.0")
+      bindPort = Port(61010)
+
+      inexistentDomain = "thisdomain.doesnot.exist"
+      invalidDomain = ""
+
+    var inexistentDomainErr, invalidDomainErr: bool = false
+
+    # Create node with inexistent domain
+    try:
+      let node = newTestWakuNode(
+        nodeKey,
+        bindIp, bindPort,
+        dns4DomainName = some(inexistentDomain))
+    except CatchableError:
+      inexistentDomainErr = true
+
+    # Create node with invalid domain
+    try:
+      let node = newTestWakuNode(
+        nodeKey,
+        bindIp, bindPort,
+        dns4DomainName = some(invalidDomain))
+    except CatchableError:
+      invalidDomainErr = true
+
+    # Check that exceptions were raised in both cases
+    check:
+      inexistentDomainErr == true
+      invalidDomainErr == true
+
   asyncTest "Agent string is set and advertised correctly":
     let
       # custom agent string