How values are generated is determined by the mode property.

Supported mode values are:

• DIGEST_MODE -- uses an empirical distribution
• REPLAY_MODE -- replays data from valuesFileURL
• UNIFORM_MODE -- generates uniformly distributed random values with mean = mu
• EXPONENTIAL_MODE -- generates exponentially distributed random values with mean = mu
• GAUSSIAN_MODE -- generates Gaussian distributed random values with mean = mu and standard deviation = sigma
• CONSTANT_MODE -- returns mu every time.