'ClassCastException class [B cannot be cast to class [C' when attempting to generate spock reports

Question

When generating unit test reports using spock-reports, I'm getting a ClassCastException:

class [B cannot be cast to class [C ([B and [C are in module java.base of loader 'bootstrap')

I'm using Java 11 with Spock 2.0 for unit tests and spock-reports (2.0.1-RC3) to generate test reports, initiated by surefire (2.22.2). I also use the spock collaborators (1.2.2) extension.

Although individual test reports are created successfully, when spock-reports tries to generate the aggregate HTML report (index.html), it gets:

c.a.s.r.internal.HtmlReportAggregator    : Failed to create aggregated report

java.lang.ClassCastException: class [B cannot be cast to class [C ([B and [C are in module java.base of loader 'bootstrap')
    at groovy.json.internal.FastStringUtils$StringImplementation$1.toCharArray(FastStringUtils.java:88) ~[groovy-all-2.3.8.jar:2.3.8]
    at groovy.json.internal.FastStringUtils.toCharArray(FastStringUtils.java:175) ~[groovy-all-2.3.8.jar:2.3.8]
    at groovy.json.internal.BaseJsonParser.parse(BaseJsonParser.java:103) ~[groovy-all-2.3.8.jar:2.3.8]
    at groovy.json.JsonSlurper.parseText(JsonSlurper.java:208) ~[groovy-all-2.3.8.jar:2.3.8]
    at groovy.json.JsonSlurper$parseText.call(Unknown Source) ~[na:na]
    at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47) ~[groovy-3.0.9.jar:3.0.9]
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125) ~[groovy-3.0.9.jar:3.0.9]
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:139) ~[groovy-3.0.9.jar:3.0.9]
    at com.athaydes.spockframework.report.internal.ReportDataAggregator$_getAllAggregatedDataAndPersistLocalData_closure1.doCall(ReportDataAggregator.groovy:44) ~[spock-reports-2.3.0-groovy-3.0.jar:2.3.0-groovy-3.0]

I can see from the stacktrace that Spock is using groovy 3.0.9 but groovy-all 2.3.8 is being pulled in (by the spock-collaborators extension).

Although I can and will investigate updating the various dependency versions, is there anything I can do in the meantime to prevent this exception so that index.html can be generated?

Answer 1

System Property

Aside from updating the other dependencies to later versions and aligning groovy versions, which ought to resolve it, a quick fix is to declare a system property:

groovy.json.faststringutils.disable=true

We can set this for our tests by adding it as a surefire systemPropertyVaribles configuration entry in pom.xml:

<plugin>
  <artifactId>maven-surefire-plugin</artifactId>
  <configuration>
    <systemPropertyVariables>
      <groovy.json.faststringutils.disable>true</groovy.json.faststringutils.disable>
    </systemPropertyVariables>
    ...
  ...
</plugin>

This was enough to get index.html generating successfully for us whilst I investigated uplifting dependency versions.

Dependency Versions

The alternative way of fixing is to uplift dependencies to the following versions (the ones you use):

• spock-reports: 2.3.0-groovy-3.0
• spock-subjects-collaborators-extension: 2.0.0
• maven-surefire-plugin: 3.0.0-M5

and add a direct groovy-all dependency (test scope, since we're only using groovy for our tests):

<dependency>
    <groupId>org.codehaus.groovy</groupId>
    <artifactId>groovy-all</artifactId>
    <version>3.0.10</version>
    <scope>test</scope>
    <type>pom</type>
</dependency>