### Question:
StudyPresentation extends PresentationModel<Study> { public int getPopulationCharacteristicCount() { return getPopulationCharacteristics().size(); } StudyPresentation(Study s, PresentationModelFactory pmf); StudyCharacteristicHolder getCharacteristicModel(Characteristic c); boolean isStudyFinished(); int getArmCount(); List<BasicArmPresentation> getArms(); int getPopulationCharacteristicCount(); List<? extends Variable> getPopulationCharacteristics(); LabeledPresentation getCharacteristicModel(BasicStudyCharacteristic c); List<OutcomeMeasure> getEndpoints(); List<OutcomeMeasure> getAdverseEvents(); PopulationCharTableModel getPopulationCharTableModel(); TableModel getEndpointTableModel(); TableModel getAdverseEventTableModel();  }### Answer:
@Test public void testGetPopulationCharacteristicCount() { d_study.createAndAddArm("arm1", 0, new Drug("X", "Y"), null); d_study.createAndAddArm("arm2", 0, new Drug("X", "Y"), null); PopulationCharacteristic age = new PopulationCharacteristic("Age", new ContinuousVariableType()); assertEquals(0, d_model.getPopulationCharacteristicCount()); d_study.getPopulationChars().clear(); d_study.getPopulationChars().addAll(Study.wrapVariables(Collections.<PopulationCharacteristic>singletonList(age))); assertEquals(1, d_model.getPopulationCharacteristicCount()); }