Error in Fuzzing test generation for code producing `Function<String, Integer>`

[alisevych]

Description

Array has more than one element error in Errors report for
Fuzzing test generation for code producing Function<String, Integer>

To Reproduce

1. Run a project with JDK 11 in IntelliJ Idea
2. Install one of the latest plugins from main
3. Set Fuzzing only mode
4. Add a Java class with the following function:

 Function<String, Integer> returnLambda(int buffer) {
 return s -> s.length() + buffer;
 }

5. Generate tests for it

Expected behavior

Tests are supposed to be generated.

Actual behavior

An error test is generated with information about errors in the concrete executor:
Array has more than one element
No exceptions are present in concrete executor log , RD engine logs, idea.log
Only one about failed to save test report.

Visual proofs (screenshots, logs, images)

import java.util.function.Function;

public final class LambdaTest {
 ///region Test suites for executable org.utbot.examples.lambda.Lambda.returnLambda

 ///region Errors report for returnLambda

 public void testReturnLambda_errors() {
 // Couldn't generate some tests. List of errors:
 // 
 // 1 occurrences of:
 // Array has more than one element.

 }
 ///endregion

 ///endregion
}

Environment

Windows 10 Pro
IntelliJ IDEA 2022.2.3
Gradle , JDK 11

Additional context

IF Symbolic execution is turned on - a successful test is generated besides the error on.

[Markoutte]

Looks like the problem is caused by this change cc @SBOne-Kenobi . The stracktrace of the error is:

java.lang.IllegalArgumentException: Array has more than one element.
	at kotlin.collections.ArraysKt___ArraysKt.single(_Arrays.kt:2812)
	at org.utbot.framework.plugin.api.UtLambdaModel.getLambdaMethodId(Api.kt:578)
	at org.utbot.framework.codegen.tree.CgVariableConstructor.constructLambda(CgVariableConstructor.kt:127)
	at org.utbot.framework.codegen.tree.CgVariableConstructor.getOrCreateVariable(CgVariableConstructor.kt:113)
	at org.utbot.framework.codegen.tree.CgMethodConstructor.generateResultAssertions(CgMethodConstructor.kt:316)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$createTestMethod$1$2$mainBody$1.invoke(CgMethodConstructor.kt:1390)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$createTestMethod$1$2$mainBody$1.invoke(CgMethodConstructor.kt:1370)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$createTestMethod$1$2.invoke(CgMethodConstructor.kt:1407)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$createTestMethod$1$2.invoke(CgMethodConstructor.kt:1363)
	at org.utbot.framework.codegen.domain.context.CgContextOwner$block$1.invoke(CgContext.kt:231)
	at org.utbot.framework.codegen.domain.context.CgContextOwner$block$1.invoke(CgContext.kt:230)
	at org.utbot.framework.codegen.domain.context.CgContextOwner$DefaultImpls.withNameScope(CgContext.kt:323)
	at org.utbot.framework.codegen.domain.context.CgContext.withNameScope(CgContext.kt:432)
	at org.utbot.framework.codegen.domain.context.CgContextOwner$DefaultImpls.block(CgContext.kt:230)
	at org.utbot.framework.codegen.domain.context.CgContext.block(CgContext.kt:432)
	at org.utbot.framework.codegen.tree.CgMethodConstructor.block(CgMethodConstructor.kt)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$testMethod$testMethod$1.invoke(CgMethodConstructor.kt:1846)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$testMethod$testMethod$1.invoke(CgMethodConstructor.kt:1843)
	at org.utbot.framework.codegen.tree.BuildersKt.buildTestMethod(Builders.kt:108)
	at org.utbot.framework.codegen.tree.CgMethodConstructor.testMethod(CgMethodConstructor.kt:1843)
	at org.utbot.framework.codegen.tree.CgMethodConstructor.testMethod$default(CgMethodConstructor.kt:1802)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$createTestMethod$1.invoke(CgMethodConstructor.kt:1363)
	at org.utbot.framework.codegen.tree.CgMethodConstructor$createTestMethod$1.invoke(CgMethodConstructor.kt:1356)
	at org.utbot.framework.codegen.tree.CgMethodConstructor.withTestMethodScope(CgMethodConstructor.kt:1717)
	at org.utbot.framework.codegen.tree.CgMethodConstructor.createTestMethod(CgMethodConstructor.kt:1356)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor.createTest(CgTestClassConstructor.kt:188)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor.constructTestSet(CgTestClassConstructor.kt:148)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$constructTestClass$1$3.invoke(CgTestClassConstructor.kt:98)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$constructTestClass$1$3.invoke(CgTestClassConstructor.kt:86)
	at org.utbot.framework.codegen.tree.BuildersKt.buildClassBody(Builders.kt:73)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$constructTestClass$1.invoke(CgTestClassConstructor.kt:86)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$constructTestClass$1.invoke(CgTestClassConstructor.kt:70)
	at org.utbot.framework.codegen.tree.BuildersKt.buildClass(Builders.kt:63)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor.constructTestClass(CgTestClassConstructor.kt:70)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$construct$1$1.invoke(CgTestClassConstructor.kt:64)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$construct$1$1.invoke(CgTestClassConstructor.kt:64)
	at org.utbot.framework.codegen.domain.context.CgContext.withTestClassScope(CgContext.kt:535)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor.withTestClassScope(CgTestClassConstructor.kt)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$construct$1.invoke(CgTestClassConstructor.kt:64)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor$construct$1.invoke(CgTestClassConstructor.kt:63)
	at org.utbot.framework.codegen.tree.BuildersKt.buildClassFile(Builders.kt:48)
	at org.utbot.framework.codegen.tree.CgTestClassConstructor.construct(CgTestClassConstructor.kt:63)
	at org.utbot.framework.codegen.CodeGenerator$generateAsStringWithTestReport$1$1.invoke(CodeGenerator.kt:74)
	at org.utbot.framework.codegen.CodeGenerator$generateAsStringWithTestReport$1$1.invoke(CodeGenerator.kt:69)
	at org.utbot.framework.codegen.domain.context.CgContext.withTestClassFileScope(CgContext.kt:525)
	at org.utbot.framework.codegen.CodeGenerator$generateAsStringWithTestReport$1.invoke(CodeGenerator.kt:69)
	at org.utbot.framework.codegen.CodeGenerator$generateAsStringWithTestReport$1.invoke(CodeGenerator.kt:68)
	at org.utbot.framework.codegen.CodeGenerator.withCustomContext(CodeGenerator.kt:98)
	at org.utbot.framework.codegen.CodeGenerator.generateAsStringWithTestReport(CodeGenerator.kt:68)
	at org.utbot.framework.codegen.CodeGenerator.generateAsStringWithTestReport$default(CodeGenerator.kt:63)
	at org.utbot.framework.process.EngineMainKt$setup$4.invoke(EngineMain.kt:154)
	at org.utbot.framework.process.EngineMainKt$setup$4.invoke(EngineMain.kt:129)
	at org.utbot.rd.CallsSynchronizer$measureExecutionForTermination$1$1.invoke(ClientProcessUtil.kt:84)
	at org.utbot.rd.CallsSynchronizer.measureExecutionForTermination(ClientProcessUtil.kt:75)
	at org.utbot.rd.CallsSynchronizer$measureExecutionForTermination$1.invoke(ClientProcessUtil.kt:83)
	at com.jetbrains.rd.framework.IRdEndpoint$set$1.invoke(TaskInterfaces.kt:182)
	at com.jetbrains.rd.framework.IRdEndpoint$set$1.invoke(TaskInterfaces.kt:182)
	at com.jetbrains.rd.framework.impl.RdCall.onWireReceived(RdTask.kt:360)
	at com.jetbrains.rd.framework.MessageBroker$invoke$2$2.invoke(MessageBroker.kt:57)
	at com.jetbrains.rd.framework.MessageBroker$invoke$2$2.invoke(MessageBroker.kt:56)
	at com.jetbrains.rd.framework.impl.ProtocolContexts.readMessageContextAndInvoke(ProtocolContexts.kt:148)
	at com.jetbrains.rd.framework.MessageBroker$invoke$2.invoke(MessageBroker.kt:56)
	at com.jetbrains.rd.framework.MessageBroker$invoke$2.invoke(MessageBroker.kt:54)
	at com.jetbrains.rd.util.threading.SingleThreadSchedulerBase.queue$lambda-3(SingleThreadScheduler.kt:41)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:829)

The problem is that functional interface has not only one abstract function but also can have default and static methods. For this case they are:

public abstract java.lang.Object java.util.function.Function.apply(java.lang.Object)
public static java.util.function.Function java.util.function.Function.identity()
public default java.util.function.Function java.util.function.Function.compose(java.util.function.Function)
public default java.util.function.Function java.util.function.Function.andThen(java.util.function.Function)
private static java.lang.Object java.util.function.Function.lambda$identity$2(java.lang.Object)
private java.lang.Object java.util.function.Function.lambda$andThen$1(java.util.function.Function,java.lang.Object)
private java.lang.Object java.util.function.Function.lambda$compose$0(java.util.function.Function,java.lang.Object)

Also, the issue is very hard to identify until CgTestClassConstructor#processFailure(testSet: CgMethodTestSet, failure: Throwable) just consumes an exception without any additional log printing. @sofurihafe Please, consider to add some error log printing.