Generating test data includes: reading values occurring in at least one field of multiple records from a data source; storing profile information including statistics characterizing the values; generating a model of a probability distribution for the field based on the statistics; generating multiple test data values using the generated model such that a frequency at which a given value occurs in the test data values corresponds to a probability assigned to that given value by the model; and storing a collection of test data including the test data values in a data storage system.