RapidMiner provides tools for validating machine learning models on test data and visualizing their performance. Validation involves splitting a labeled dataset into training and test sets to evaluate how well a model trained on one set predicts the other. RapidMiner operators measure performance by comparing a model's predicted labels to true labels on the test set. Visualization tools like SOM plots further analyze models by transforming data dimensions and coloring results based on a model's predictions, helping users understand model quality and characteristics before deployment.