Remove obsolete fuzzing code and update readme.md #467 (#530)

Author: Markoutte

utbot-fuzzers/readme.md

@@ -1,36 +1,66 @@
 # UTBot Fuzzer
 
-Fuzzer generates method input values to improve method coverage or find unexpected errors. In UTBot next strategies can be used to find those values:
+Fuzzer generates method input values to improve method coverage or find unexpected errors. In UTBot next strategies can be used to find values like:
 
 * **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.
+* **Corner case 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.
+* **Objects** created via its constructors or field mutators.
+
+After values are found fuzzer creates all its possible combinations and runs methods with these combinations.
+
+For example, if a method has two parameters of types `boolean` and `int` the follow values can be found:
+```
+boolean = [false, true]
+int = [0, MAX_VALUE, MIN_VALUE]
+```
+
+Now, fuzzer creates `2 * 3 = 6` combinations of them:
+
+```
+[false, 0], [false, MAX_VALUE], [false, MIN_VALUE], [true, 0], [true, MAX_VALUE], [true, MIN_VALUE]
+```
+
+To find more branches of execution as fast as possible fuzzer also shuffles
+combinations and supplies them for the running.
 
 ## Design
 
-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 requires model providers that create a set of `UtModel` for a given `ClassId`. 
+Fuzzer iterates through these providers and creates models, which are used for generating combinations later. 
+Each combination contains concrete values that can be accepted by the method. 
+For example, if a method has signature with `String, double, int` as parameters then fuzzer can create combination `"sometext", Double.POSITIVE_INFINITY, 0`.  
 
 Fuzzer's entry point is:
 ```kotlin
 // org.utbot.fuzzer.FuzzerKt
-fun fuzz(method: FuzzedMethodDescription, vararg models: ModelProvider): Sequence<List<UtModel>>
+fun fuzz(method: FuzzedMethodDescription, vararg models: ModelProvider): Sequence<List<FuzzedValue>>
 ```
 
+`FuzzedMethodDescription` stores comprehensive information about a method:
+* signature (parameters and return types)
+* name/package/class (optional)
+* constants found in the method body (should be replaced with CGF when possible)
+
+`ModelProvider` provides models for a give parameters set as described below.
+
+Fuzz method returns a sequence of acceptable values for the method in random order. The sequence is lazy.
+
 Model provider should implement
 
 ```kotlin
-fun generate(description: FuzzedMethodDescription, consumer: BiConsumer<Int, UtModel>)
+fun generate(description: FuzzedMethodDescription): Sequence<FuzzedParameter>
 ```
-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)`.
+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:
 
 ```kotlin
 ObjectModelProvider()
     .with(PrimitiveModelProvider)
     // ...
-    .with(NullModelProvider)
+    .with(ObjectModelProvider)
     .withFallback { classId ->
         createDefaultModelByClass(classID)
     }
@@ -39,24 +69,138 @@ or
 
 ```kotlin
 // org.utbot.fuzzer.FuzzerKt
-fun defaultModelProviders(idGenerator: ToIntFunction<ClassId>)
+fun defaultModelProviders(idGenerator: IntSupplier)
 ```
 
-## List of builtin Providers
+## List of builtin providers
+
+### PrimitiveDefaultsModelProvider
+
+Creates default values for every primitive types:
+
+```
+boolean: false
+byte: 0
+short: 0
+int: 0
+long: 0
+float: 0.0
+double: 0.0
+char: \u0000
+string: ""
+```
 
 ### PrimitiveModelProvider
 
 Creates default values and some corner case values such as Integer.MAX_VALUE, 0.0, Double.NaN, empty string, etc.
 
+```
+boolean: false, true
+byte: 0, 1, -1, Byte.MIN_VALUE, Byte.MAX_VALUE
+short: 0, 1, -1, Short.MIN_VALUE, Short.MAX_VALUE
+int: 0, 1, -1, Integer.MIN_VALUE, Integer.MAX_VALUE
+long: 0, 1, -1, Long.MIN_VALUE, Long.MAX_VALUE
+float: 0.0, 1.1, -1.1, Float.MIN_VALUE, Float.MAX_VALUE, Float.NEGATIVE_INFINITY, Float.POSITIVE_INFINITY, Float.NaN
+double: 0.0, 1.1, -1.1, Double.MIN_VALUE, Double.MAX_VALUE, Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY, Double.NaN
+char: Char.MIN_VALUE, Char.MAX_VALUE
+string: "", "   ", "string", "\n\t\r"
+```
+
+### PrimitiveWrapperModelProvider
+
+Creates primitive models for boxed types: `Boolean`, `Byte`, `Short`, `Integer`, `Long`, `Double`, `Float`, `Character`, `String` 
+
 ### ConstantsModelProvider
 
 Uses information about concrete values from `FuzzedMethodDescription#concreteValues` to generate simple values.
-At the moment, only primitive values are supported.
+Only primitive values are supported.
+
+### NullModelProvider
+
+Creates `UtNullModel` for every reference class.
+
+### EnumModelProvider
+
+Creates models for any enum type.
+
+### CollectionModelProvider
+
+Creates concrete collections for collection interfaces: `List`, `Set`, `Map`, `Collection`, `Iterable`, `Iterator`
+
+### ArrayModelProvider
+
+Creates an empty and non-empty for any type.
 
 ### ObjectModelProvider
 
-Creates models of class that has public constructor with primitives as parameters only. 
+ObjectModelProvider is the most sophisticated provider. It creates model of class that has public constructors 
+and public mutators (fields or setters/getters). If class has constructor that accepts another object within an argument that value 
+is created recursively. Depth of recursion is limited to 1. Thus, for inner object fuzzing doesn't try to use every
+constructor but find the one with the least number of parameters and, if it is possible, only
+constructor with primitives values. If there is available only constructor with another object as a parameter then
+`null` is passed to it.
+
+Let's look at this example:
+
+```java
+class A {
+    private int a;
+    private Object object;
+    
+    public A(int a, A o) {
+        this.a = a;
+        this.o = o;
+    }
+}
+```
 
-### NullModelProvider
+For it fuzzing create these models:
+```
+new Object(0, new A(0, null));
+new Object(Integer.MIN_VALUE, new A(0, null));
+new Object(Integer.MAX_VALUE, new A(0, null));
+new Object(0, new A(Integer.MIN_VALUE, null));
+new Object(Integer.MIN_VALUE, new A(Integer.MIN_VALUE, null));
+new Object(Integer.MAX_VALUE, new A(Integer.MIN_VALUE, null));
+new Object(0, new A(Integer.MAX_VALUE, null));
+new Object(Integer.MIN_VALUE, new A(Integer.MAX_VALUE, null));
+new Object(Integer.MAX_VALUE, new A(Integer.MAX_VALUE, null));
+```
+
+For classes that have empty public constructor and field mutators all those mutators will be fuzzed as well.
+Field mutators are listed below:
+* public or package-private (and accessible) non-final non-static fields
+* pairs of setter/getter that satisfy the common agreement:
+  * setter/getter is public or package-private (and accessible)
+  * have field name as a postfix, e.g.: `int myField -> * setMyField(int v)/int getMyField()`, where * means any returned type
+
+For example, fields _a_, _b_ and _d_ will be fuzzed, but _c_ and _e_ will not:
+
+```java
+class A {
+    int a;
+    public char b;
+    public final int c = 0;
+    private String d;
+    private boolean e;
+    
+    public A setD(String s) {
+        this.d = s;
+        return this;
+    }
+    
+    public String getD() {
+        return d;
+    }
+    
+    public boolean getE() {
+        return e;
+    }
+}
+```
+
+### Other providers
 
-Creates `UtNullModel` for every reference class.
+There are several other providers that can find some values, using addition information, 
+like `CharToStringModelProvider` that takes all chars found in `charAt(i) == c` statement
+and merge them into several strings.