unit testing - Spock mocks showing up as nulls -

here main class:

@slf4j class consolereaderworker implements runnable {     consolereader reader     writer writer     remotecommandselector commandselector      @inject     consolereaderworker(consolereader reader, writer writer, remotecommandselector commandselector) {         super()         this.reader = reader         this.writer = writer         this.commandselector = commandselector     }      @override     void run() {         try {             string line             while ((line = reader.readline()) != null) {                 commandselector.select(line).execute(writer)                 writer.flush()             }         } catch(interruptedexception ex) {             log.warn("${this} interrupted with: ${exceptionutils.getstacktrace(ex)}")         }     } } 

here attempt @ spock specification class:

class consolereaderworkerspec extends specification {     def "when enter key pressed command selected , executed , writer flushed"() {         given: "a running fixture mock dependencies"         consolereader reader = mock(consolereader)         writer writer = mock(writer)         remotecommand command = mock(remotecommand)         remotecommandselector commandselector = mock(remotecommandselector)          reader.readline() >> '\n'         commandselector.select(_) >> command          consolereaderworker worker = new consolereaderworker(reader, writer, commandselector)          when: "the enter key pressed"         worker.run()          then: "a command executed"         1 * commandselector.select(_)     } } 

essentially, want confirm when run() method invoked, commandselector#select() method invoked any argument.

when run get:

java.lang.nullpointerexception: cannot invoke method execute() on null object     @ com.nocbots.nbsvc.remote.cli.jline.consolereaderworker.run(consolereaderworker.groovy:33)     @ com.nocbots.nbsvc.remote.cli.jline.consolereaderworkerspec.when enter key pressed command selected , executed , writer flushed(consolereaderworkerspec.groovy:25) 

line 33 of consolereadyworker call commandselector.select() lives inside while loop:

commandselector.select(line).execute(writer) 

any ideas why?!? can see, i've wired commandselector#select() mock return remotecommand mock, should never null...ideas?

try:

then: "a command executed" 1 * commandselector.select(_) >> command 

instead of:

commandselector.select(_) >> command 

please have @ docs. when both mock , verify, then block should used.

edit

this spock related error you're getting, trust me. have @ runnable script below (can run using groovy console):

@grab('org.spockframework:spock-core:1.0-groovy-2.4') @grab('cglib:cglib-nodep:3.1')  import spock.lang.*  class consolereaderworkerspec extends specification {     def "when enter key pressed command selected , executed , writer flushed"() {         given: "a running fixture mock dependencies"         consolereader reader = mock(consolereader)         writer writer = mock(writer)         remotecommand command = mock(remotecommand)         remotecommandselector commandselector = mock(remotecommandselector)          reader.readline() >> '\n'          consolereaderworker worker = new consolereaderworker(reader, writer, commandselector)          when: "the enter key pressed"         worker.run()          then: "a command executed"         1 * commandselector.select(_) >> command     } }  class consolereaderworker implements runnable {      consolereader reader     writer writer     remotecommandselector commandselector      consolereaderworker(consolereader reader, writer writer, remotecommandselector commandselector) {         this.reader = reader         this.writer = writer         this.commandselector = commandselector     }      @override     void run() {         try {             string line             while ((line = reader.readline()) != null) {                 commandselector.select(line).execute(writer)                 writer.flush()             }         } catch(interruptedexception ex) {             log.warn("${this} interrupted with: ${exceptionutils.getstacktrace(ex)}")         }     } } class writer {    void flush() {} } class remotecommand {    void execute(writer w) {     } } class consolereader {    string readline() {       ''    } } class remotecommandselector {    remotecommand select(o) {       new remotecommand()    } } 

it fails since select invoked twice, not fail npe. fix add following line:

reader.readline() >>> ['\n', null]