More explicit class test, add tests

Author: swallez

java-client/src/main/java/co/elastic/clients/json/JsonpUtils.java

@@ -70,11 +70,11 @@ public static void setProvider(JsonProvider provider) {
     static JsonProvider findProvider() {
         try {
             // Default to Jackson
+            Class.forName("com.fasterxml.jackson.databind.ObjectMapper");
             return new JacksonJsonProvider();
-        } catch (NoClassDefFoundError e) {
-            // Ignore
+        } catch (ClassNotFoundException e) {
+            return findSystemProvider();
         }
-        return findSystemProvider();
     }
 
     /**

java-client/src/test/java/co/elastic/clients/json/JsonpUtilsTest.java

@@ -20,6 +20,7 @@
 package co.elastic.clients.json;
 
 import co.elastic.clients.elasticsearch.core.search.Hit;
+import co.elastic.clients.json.jackson.JacksonJsonProvider;
 import co.elastic.clients.testkit.ModelTestCase;
 import co.elastic.clients.elasticsearch.security.IndexPrivilege;
 import co.elastic.clients.elasticsearch.security.IndicesPrivileges;
@@ -84,6 +85,15 @@ public void testObjectToString() {
         assertEquals("Hit: {\"_index\":\"idx\",\"_id\":\"id1\",\"_source\":\"Some user data\"}", hit.toString());
     }
 
+    @Test
+    public void testDefaultProvider() {
+        // Provider defaults to Jackson
+        assertTrue(JsonpUtils.provider() instanceof JacksonJsonProvider);
+
+        // System provider uses service lookup
+        assertFalse(JsonpUtils.systemProvider() instanceof JacksonJsonProvider);
+    }
+
     private static class SomeUserData {
         @Override
         public String toString() {