Spock Error:Groovyc: Could not instantiate global transform class

I m new to Spock, tried to write a simple Spock but it failed:

Error:Groovyc: Could not instantiate global transform class org.spockframework.compiler.SpockTransform specified at jar:file:.../.m2/repository/org/spockframework/spock-core/1.0-groovy-2.4/spock-core-1.0-groovy-2.4.jar!/META-INF/services/org.codehaus.groovy.transform.ASTTransformation  because of exception java.lang.NullPointerException

here is my Spec:

@Unroll
class UserFilterSpec extends Specification {
    private static final String USER_ID_1 = "someUserId1";
    private static final String USER_ID_2 = "someUserId2";
    private static final String USER_ID_3 = "someUserId3";

    def filter = new UserFilter()

    def User user1 = setupTestUser(USER_ID_1)
    def User user2 = setupTestUser(USER_ID_2)
    def User user3 = setupTestUser(USER_ID_3)

    def "given a list of users and list of user ids, should return list of user with those users removed"() {
        expect:
        filter.filterUserDataByIds(userList, userIdList) == filterList

        where:
        userList                                | userIdList                    || filterList
        Lists.newArrayList(user1, user2, user3) | Lists.newArrayList(USER_ID_1) || Lists.newArrayList(user2, user3)

    }
}

and here is my pom.xml:

<!-- Mandatory plugins for using Spock -->
            <plugin>
              <!-- The gmavenplus plugin is used to compile Groovy code. To learn more about this plugin,
              visit https://github.com/groovy/GMavenPlus/wiki -->
              <groupId>org.codehaus.gmavenplus</groupId>
              <artifactId>gmavenplus-plugin</artifactId>
              <version>1.4</version>
              <executions>
                <execution>
                  <goals>
                    <goal>compile</goal>
                    <goal>testCompile</goal>
                  </goals>
                </execution>
              </executions>
            </plugin>
            <!-- Optional plugins for using Spock -->
            <!-- Only required if names of spec classes don't match default Surefire patterns (`*Test` etc.) -->
            <plugin>
              <artifactId>maven-surefire-plugin</artifactId>
              <version>2.6</version>
              <configuration>
                <useFile>false</useFile>
                <includes>
                  <include>**/*Spec.java</include>
                  <include>**/*Test.java</include> <!-- Just in case of having also "normal" JUnit tests -->
                </includes>
              </configuration>
            </plugin>

...
    <!-- Mandatory dependencies for using Spock -->
    <dependency>
      <groupId>org.spockframework</groupId>
      <artifactId>spock-core</artifactId>
      <version>1.0-groovy-2.4</version>
      <scope>test</scope>
    </dependency>
    <!-- Optional dependencies for using Spock -->
    <dependency> <!-- use a specific Groovy version rather than the one specified by spock-core -->
      <groupId>org.codehaus.groovy</groupId>
      <artifactId>groovy-all</artifactId>
      <version>2.4.1</version>
    </dependency>
    <dependency> <!-- enables mocking of classes (in addition to interfaces) -->
      <groupId>cglib</groupId>
      <artifactId>cglib-nodep</artifactId>
      <version>3.1</version>
      <scope>test</scope>
    </dependency>
    <dependency> <!-- enables mocking of classes without default constructor (together with CGLIB) -->
      <groupId>org.objenesis</groupId>
      <artifactId>objenesis</artifactId>
      <version>2.1</version>
      <scope>test</scope>
    </dependency>

what is wrong my Spec or pom setting? do i have to install Groovy to make it work?

Answer

Here is your test, re-written in more idiomatic Spock/Groovy:

@Unroll
class UserFilterSpec extends Specification {
    static final String USER_ID_1 = "someUserId1"
    static final String USER_ID_2 = "someUserId2"
    static final String USER_ID_3 = "someUserId3"

    @Shared user1 = setupTestUser(USER_ID_1)
    @Shared user2 = setupTestUser(USER_ID_2)
    @Shared user3 = setupTestUser(USER_ID_3)

    @Shared filter = new UserFilter()

    def "given a list of users and list of user ids, should return list of user with those users removed"() {
        expect:
        filter.filterUserDataByIds(userList, userIdList) == filterList

        where:
        userList              | userIdList  || filterList
        [user1, user2, user3] | [USER_ID_1] || [user2, user3]    
    }
}

A couple of notes:

• Groovy (in which Spock tests are written) has native support for declaring collections. Thus [user1, user3] instead of Lists.newArrayList.
• @Shared or static is required for class-level variables that are used in tests. This will solve your compilation problem.
• I highly recommend reading the Groovy user guide, it’s a great read and will help you immensely getting started with Spock. The style guide is here: http://www.groovy-lang.org/style-guide.html, and from there you can explore the Documentation page for other interesting tidbits.
• The Spock documentation is also excellent, and can easily be read in one sitting: http://docs.spockframework.org.