Refactor the SimpleTestRunner and its test.

src/main/java/space/kklochko/simple_jbdd/tests/runners/SimpleTestRunner.java

@@ -4,10 +4,10 @@ import space.kklochko.simple_jbdd.tests.Test;
 import space.kklochko.simple_jbdd.tests.commands.AbstractTestCommand;
 
 public class SimpleTestRunner extends AbstractTestRunner {
-    AbstractTestCommand<Test> command;
+    private AbstractTestCommand<Test> command;
 
     public SimpleTestRunner(AbstractTestCommand<Test> command) {
-        this.command = command;
+        setCommand(command);
     }
 
     public boolean run() {

src/test/groovy/space/kklochko/simple_jbdd/tests/runners/SimpleTestRunnerSpec.groovy

@@ -40,7 +40,7 @@ class SimpleTestRunnerSpec extends Specification {
         when: "The testCommand has been run"
         def result = runner.run()
 
-        then: "The result is true"
+        then: "The result is false"
         !result
     }
 }