Seeking to understand properties

[Steve Huston]

I am struggling to understand something I fear is very basic, but I just don't 
see it. Hoping someone can help me understand this.

Properties... I can use them in route definitions, but I don't seem to be able 
to obtain their values in regular Java code.

Example (using Camel 2.16.3):

I have a route builder:

public class MyRouteBuilder extends RouteBuilder {
    public void configure() {
        from("file:{{dataFile}}?noop=true")
         .to("file:target/messages/others");
    }
}

And a unit test:

@RunWith(JUnit4.class)
public class UnitTest extends CamelTestSupport {

        private String fileName;

            @Override
            protected RouteBuilder createRouteBuilder() {
                return new MyRouteBuilder();
            }

            @Override
            public Boolean ignoreMissingLocationWithPropertiesComponent() {
                return true;
            }

            @Override
            protected Properties useOverridePropertiesWithPropertiesComponent() 
{
                    Properties override = new Properties();
                    override.put("dataFile", "overridden-file");
                    return override;
            }

            @Test
                public void testPropertyGetting() throws Exception {
                fileName = context().getProperty("dataFile");
                assert(fileName != null);
            }
}

When I run this test, the output includes:

INFO  Route: route1 started and consuming from: 
Endpoint[file://overridden-file?noop=true]

So the override property set above did get filled into the route definition.
However, when I try to get the property in the testPropertyGetting() method, 
the value is null

Why???

-Steve