java.io.FileNotFoundException: /jacoco.exec: open failed: EROFS (Read-only file system)

Question

Facing this problem while trying to implement JaCoCo Offline Instrumentation.

W/System.err( 1733): java.io.FileNotFoundException: /jacoco.exec: open failed: EROFS (Read-only file system)
W/System.err( 1733):    at libcore.io.IoBridge.open(IoBridge.java:456)
W/System.err( 1733):    at java.io.FileOutputStream.<init>(FileOutputStream.java:89)
--
W/System.err( 1733):    at libcore.io.IoBridge.open(IoBridge.java:456)
W/System.err( 1733):    at java.io.FileOutputStream.<init>(FileOutputStream.java:89)
W/System.err( 1733):    at org.jacoco.agent.rt.internal_14f7ee5.output.FileOutput.openFile(FileOutput.java:67)
W/System.err( 1733):    at org.jacoco.agent.rt.internal_14f7ee5.output.FileOutput.startup(FileOutput.java:49)
W/System.err( 1733):    at org.jacoco.agent.rt.internal_14f7ee5.Agent.startup(Agent.java:122)
W/System.err( 1733):    at org.jacoco.agent.rt.internal_14f7ee5.Agent.getInstance(Agent.java:50)
W/System.err( 1733):    at org.jacoco.agent.rt.internal_14f7ee5.Offline.<clinit>(Offline.java:31)

Answer 1

The solution is well-documented in jacoco but for Android people, what you need is to add the file in /src/androidTest/resources/jacoco-agent.properties with the contents output=none so jacoco can startup without failing, and coverage will be written as normal and transferred correctly later by the android gradle plugin coverage implementation.

Answer 2

I think it's safe to ignore that offline instrumentation warning, because the path should be something alike: executionData = files("${project.buildDir}/jacoco/${testTaskName}.exec") (on the PC - so there is no need to save it on the device and then pull the file).

---

On Android this will add the JaCoCo agent into the APK:

buildTypes {
    debug {
        testCoverageEnabled = true
    }
}