Fuzzer generates method input values to improve method coverage or find unexpected errors. In UTBot next strategies can be used to find those values:

• Default values for objects, e.g. 0, 0.0, empty string or null values.
• Bound values of primitives types, e.g. Integer.MAX_VALUE, Double.POSITIVE_INFINITY, etc.
• Method constants and their simple mutations of primitive types.
• Simple objects created via its constructors.

Fuzzer requires model providers which are a simple functions to create a set of UtModel for a given ClassId. Fuzzer iterates through these providers and creates models, which are used for generating all possible combinations. Each combination contains values for the method. For example, if a method has String, double, int as parameters then fuzzer can create combination "sometext", Double.POSITIVE_INFINITY, 0.

Fuzzer's entry point is:

// org.utbot.fuzzer.FuzzerKt
fun fuzz(method: FuzzedMethodDescription, vararg models: ModelProvider): Sequence<List<UtModel>>

Model provider should implement

fun generate(description: FuzzedMethodDescription, consumer: BiConsumer<Int, UtModel>)

where consumer accepts 2 values: index of a parameter for the method and model for this parameter. For every parameter should exist at least one UtModel. ModelProvider.withFallback can be used to process those classes which cannot be processed by provider. Several providers can be combined into one by using ModelProvider.with(anotherModel: ModelProvider).

Common way to generate all combinations is:

ObjectModelProvider()
    .with(PrimitiveModelProvider)
    // ...
    .with(NullModelProvider)
    .withFallback { classId ->
        createDefaultModelByClass(classID)
    }

or

// org.utbot.fuzzer.FuzzerKt
fun defaultModelProviders(idGenerator: ToIntFunction<ClassId>)

Creates default values and some corner case values such as Integer.MAX_VALUE, 0.0, Double.NaN, empty string, etc.

Uses information about concrete values from FuzzedMethodDescription#concreteValues to generate simple values. At the moment, only primitive values are supported.

Creates models of class that has public constructor with primitives as parameters only.

Creates UtNullModel for every reference class.