Properly create void models (for mocking void methods)

Author: IlyaMuravjov

utbot-framework-api/src/main/kotlin/org/utbot/framework/plugin/api/util/IdUtil.kt

@@ -11,6 +11,7 @@ import org.utbot.framework.plugin.api.MethodId
 import org.utbot.framework.plugin.api.UtModel
 import org.utbot.framework.plugin.api.UtNullModel
 import org.utbot.framework.plugin.api.UtPrimitiveModel
+import org.utbot.framework.plugin.api.UtVoidModel
 import org.utbot.framework.plugin.api.id
 import soot.SootField
 import java.lang.reflect.Constructor
@@ -449,6 +450,7 @@ fun ClassId.defaultValueModel(): UtModel = when (this) {
     doubleClassId -> UtPrimitiveModel(0.0)
     booleanClassId -> UtPrimitiveModel(false)
     charClassId -> UtPrimitiveModel('\u0000')
+    voidClassId -> UtVoidModel
     else -> UtNullModel(this)
 }
 

utbot-java-fuzzing/src/main/kotlin/org/utbot/fuzzing/JavaLanguage.kt

@@ -50,6 +50,7 @@ fun defaultValueProviders(idGenerator: IdentityPreservingIdGenerator<Int>) = lis
     IteratorValueProvider(idGenerator),
     EmptyCollectionValueProvider(idGenerator),
     DateValueProvider(idGenerator),
+    VoidValueProvider,
     NullValueProvider,
 )
 

utbot-java-fuzzing/src/main/kotlin/org/utbot/fuzzing/providers/Primitives.kt

@@ -2,6 +2,7 @@ package org.utbot.fuzzing.providers
 
 import org.utbot.framework.plugin.api.ClassId
 import org.utbot.framework.plugin.api.UtPrimitiveModel
+import org.utbot.framework.plugin.api.UtVoidModel
 import org.utbot.framework.plugin.api.util.*
 import org.utbot.fuzzer.FuzzedContext
 import org.utbot.fuzzer.FuzzedContext.Comparison.*
@@ -236,4 +237,9 @@ object StringValueProvider : PrimitiveValueProvider(stringClassId, java.lang.Cha
             else -> false
         }
     }
+}
+
+object VoidValueProvider : PrimitiveValueProvider(voidClassId) {
+    override fun generate(description: FuzzedDescription, type: FuzzedType): Sequence<Seed<FuzzedType, FuzzedValue>> =
+        sequenceOf(Seed.Simple(UtVoidModel.fuzzed { summary = "%var% = void" }))
 }