Add comma-separated example

spring-5-webflux/src/test/java/com/baeldung/spring/webclientrequests/WebClientRequestsUnitTest.java

@@ -131,6 +131,7 @@ public class WebClientRequestsUnitTest {
         verifyCalledUrl("/posts/?tag%5B%5D=Spring&tag%5B%5D=Kotlin");
     }
 
+
     @Test
     public void whenCallArrayQueryParams_thenURIMatched() {
         this.webClient.get()
@@ -142,6 +143,17 @@ public class WebClientRequestsUnitTest {
         verifyCalledUrl("/posts/?category=Web&category=Mobile");
     }
 
+    @Test
+    public void whenCallArrayQueryParamsComma_thenURIMatched() {
+        this.webClient.get()
+                .uri(uriBuilder -> uriBuilder
+                        .path("/posts/")
+                        .queryParam("category",  String.join(",", "Web", "Mobile"))
+                        .build())
+                .retrieve();
+        verifyCalledUrl("/posts/?category=Web,Mobile");
+    }
+
     private void verifyCalledUrl(String relativeUrl) {
         ClientRequest request = this.argumentCaptor.getValue();
         Assert.assertEquals(String.format("%s%s", BASE_URL, relativeUrl), request.url().toString());