Revise CustomObjectValue test expected result

The defaultValue was the same as the value returned by the
CustomObject class, so it was not clear which result was being
returned.

Changed the return value from the CustomObject class to be clearly
different from the default value.

src/test/java/org/jenkinsci/plugins/badge/extensions/BuildParameterResolverExtensionTest.java

@@ -30,9 +30,15 @@ void setUp() {
 
     // A custom class to control the toString() behavior
     private static class CustomObject {
+        final String returnValue;
+
+        CustomObject(String returnValue) {
+            this.returnValue = returnValue;
+        }
+
         @Override
         public String toString() {
-            return "default";
+            return returnValue;
         }
     }
 
@@ -93,17 +99,18 @@ void resolveShouldReplaceParameterWithDefaultValueIfParamValueIsNull() {
     }
 
     @Test
-    void resolveShouldReplaceParameterWithDefaultValueIfParamValueToStringIsNull() {
+    void resolveShouldReplaceParameterWithCustomObjectValueIfParamValueToStringIsNull() {
         String paramName = "paramName";
         String defaultValue = "default";
         String parameter = "params." + paramName + "|" + defaultValue;
+        String customObjectReturnValue = defaultValue + "CustomObject";
 
         ParameterValue valueMock = mock(ParameterValue.class);
-        when(valueMock.getValue()).thenReturn(new CustomObject());
+        when(valueMock.getValue()).thenReturn(new CustomObject(customObjectReturnValue));
 
         when(paramsMock.getParameter(paramName)).thenReturn(valueMock);
         when(runMock.getAction(ParametersAction.class)).thenReturn(paramsMock);
 
-        assertEquals(defaultValue, resolver.resolve(runMock, parameter));
+        assertEquals(customObjectReturnValue, resolver.resolve(runMock, parameter));
     }
 }