test(schema): enforce exception behavior when joining empty query parameter maps

- align test expectations with stricter QueryParamEnum validation

Signed-off-by: Yoham Gabriel B. @Urbine <yohamg@programmer.net>

Author: Urbine

src/test/java/net/ygbstudio/powerwp4j/models/schema/WPQueryParamTest.java

@@ -1,7 +1,7 @@
 package net.ygbstudio.powerwp4j.models.schema;
 
+import static org.assertj.core.api.Assertions.assertThatException;
 import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.Matchers.is;
 
 import java.util.Collections;
 import java.util.LinkedHashMap;
@@ -48,7 +48,8 @@ void joinQueryParamsWithTimestamp() {
 
   @Test
   void joinQueryParamEmptyMapTest() {
-    String resultingPath = QueryParamEnum.joinQueryParams(Collections.emptyMap());
-    assertThat(resultingPath, is(""));
+    assertThatException()
+        .isThrownBy(() -> QueryParamEnum.joinQueryParams(Collections.emptyMap()))
+        .isInstanceOf(IllegalArgumentException.class);
   }
 }