I learned supervised classification through the example of Google Earth Engine, but in this example, I found that I cannot use Map.addLayer () to visualize the training data and test data. When I use this code:
        Map.addLayer (trainingPartition, {'color': '# ff0000'}, 'train');
        Map.addLayer (testingPartition, {'color': '# 3b8b00'}, 'test');**
        Nothing appears on the screen. 
        Does anyone know why this is the case?
        Here are  Key codes:
        // Optionally, do some accuracy assessment.  Fist, add a column of
        // random uniforms to the training dataset.
        var withRandom = training.randomColumn('random');
        // We want to reserve some of the data for testing, to avoid overfitting the model.
        var split = 0.7;  // Roughly 70% training, 30% testing.
        var trainingPartition = withRandom.filter(ee.Filter.lt('random', split));
        var testingPartition = withRandom.filter(ee.Filter.gte('random', split));
        Map.addLayer(trainingPartition,{'color':'#ff0000'},'train')
        Map.addLayer(testingPartition,{'color':'#3b8b00'},'test')
        
        Here is link:
        https://code.earthengine.google.com/1c2f985baf131e88b3dd96fbbab9b588