Incorrect Jacoco code coverage for Kotlin coroutine

Question

I am using Jacoco for unit test code coverage. Jacoco's generated report shows that few branches are missed in my Kotlin code. I noticed that the coroutine code and the code after it, is not properly covered according to Jacoco. I am not sure if it is because of coroutine or something else. While running my unit test with the IntelliJ Code Coverage my Kotlin class shows 100% coverage.

I don't know why Jacoco is showing lesser coverage. I have written my Unit Tests using Spock (Groovy).

Please refer the below images:

Missed Branches:

Original Code:

Answer 1

Similarly to "Why is JaCoCo not covering my String switch statements?" :

JaCoCo performs analysis of bytecode, not source code. Compilation of Example.kt with kotlinc 1.3.10

package example

fun main(args: Array<String>) {
    kotlinx.coroutines.runBlocking { // line 4
    }
}

results in two files ExampleKt.class and ExampleKt$main$1.class, bytecode of last one (javap -v -p ExampleKt$main$1.class) contains method invokeSuspend(Object)

  public final java.lang.Object invokeSuspend(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
    flags: ACC_PUBLIC, ACC_FINAL
    Code:
      stack=3, locals=4, args_size=2
         0: invokestatic  #29                 // Method kotlin/coroutines/intrinsics/IntrinsicsKt.getCOROUTINE_SUSPENDED:()Ljava/lang/Object;
         3: astore_3
         4: aload_0
         5: getfield      #33                 // Field label:I
         8: tableswitch   { // 0 to 0
                       0: 28
                 default: 53
            }
        28: aload_1
        29: dup
        30: instanceof    #35                 // class kotlin/Result$Failure
        33: ifeq          43
        36: checkcast     #35                 // class kotlin/Result$Failure
        39: getfield      #39                 // Field kotlin/Result$Failure.exception:Ljava/lang/Throwable;
        42: athrow
        43: pop
        44: aload_0
        45: getfield      #41                 // Field p$:Lkotlinx/coroutines/CoroutineScope;
        48: astore_2
        49: getstatic     #47                 // Field kotlin/Unit.INSTANCE:Lkotlin/Unit;
        52: areturn
        53: new           #49                 // class java/lang/IllegalStateException
        56: dup
        57: ldc           #51                 // String call to 'resume' before 'invoke' with coroutine
        59: invokespecial #55                 // Method java/lang/IllegalStateException."<init>":(Ljava/lang/String;)V
        62: athrow
      LineNumberTable:
        line 4: 3
        line 5: 49

which is associated with line 4 of source file and contains branches (ifeq, tableswitch).

While latest as of today JaCoCo version (0.8.2) has filters for various compiler-generated artifacts such as String in switch statement, bytecode that Kotlin compiler generates for coroutines is not filtered. Changelog can be seen at https://www.jacoco.org/jacoco/trunk/doc/changes.html And among others at https://www.jacoco.org/research/index.html there is also presentation about bytecode pattern matching that shows/explains many compiler-generated artifacts.

---

What you see in IntelliJ IDEA as 100% - is only line coverage, so you are trying to compare two completely different things. As a proof - here is screenshot of IntelliJ IDEA which shows 100% line coverage, but only one branch of if was executed (where args.size >= 0 evaluates to true)

And here is corresponding screenshots of JaCoCo report for execution of the same source file

Going up to the package level you can see 100% line coverage, but 50% branch coverage

And then going down to the class level via the first link ExampleKt.main.new Function2() {...} you can again see that method invokeSuspend(Object) contributes missed branches

---

Update (29/01/2019)

JaCoCo version 0.8.3 has filter for branches added by the Kotlin compiler for suspending lambdas and functions:

Answer 2

Jacoco version 0.8.3 fixes it, it has been released yesterday January 24th.

Full change-log can be found here: https://github.com/jacoco/jacoco/releases