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  package org.apache.cayenne.access.translator.select;
  
  import org.apache.cayenne.access.sqlbuilder.sqltree.ColumnNode;
  import org.apache.cayenne.access.sqlbuilder.sqltree.EmptyNode;
  import org.apache.cayenne.access.sqlbuilder.sqltree.GroupByNode;
  import org.apache.cayenne.access.sqlbuilder.sqltree.Node;
  import org.apache.cayenne.exp.path.CayennePath;
  import org.apache.cayenne.exp.property.PropertyFactory;
  import org.junit.Before;
  import org.junit.Test;
  
  import static org.hamcrest.CoreMatchers.instanceOf;
  import static org.hamcrest.MatcherAssert.assertThat;
  import static org.junit.Assert.*;
  
  /**
   * @since 4.2
   */
  public class GroupByStageTest {
  
      private TranslatorContext context;
  
      @Before
      public void prepareContext() {
          TranslatableQueryWrapper wrapper = new MockQueryWrapperBuilder().build();
          context = new MockTranslatorContext(wrapper);
      }
  
      // no result columns
      @Test
      public void emptyContext() {
          GroupByStage stage = new GroupByStage();
          stage.perform(context);
  
          Node node = context.getSelectBuilder().build();
          assertEquals(0, node.getChildrenCount());
      }
  
      // result column but no aggregates
      @Test
      public void noAggregates() {
          context.addResultNode(new ColumnNode("t0", "column", null, null));
  
          GroupByStage stage = new GroupByStage();
          stage.perform(context);
  
          Node node = context.getSelectBuilder().build();
          assertEquals(0, node.getChildrenCount());
      }
  
      // result column + aggregate
      @Test
      public void groupByWithAggregates() {
          context.addResultNode(new ColumnNode("t0", "column", null, null));
          context.addResultNode(new EmptyNode(), true, PropertyFactory.COUNT, CayennePath.of("count"));
  
          GroupByStage stage = new GroupByStage();
          stage.perform(context);
  
          Node node = context.getSelectBuilder().build();
          assertEquals(1, node.getChildrenCount());
          assertThat(node.getChild(0), instanceOf(GroupByNode.class));
          assertEquals(1, node.getChild(0).getChildrenCount());
          assertThat(node.getChild(0).getChild(0), instanceOf(ColumnNode.class));
          ColumnNode columnNode = (ColumnNode)node.getChild(0).getChild(0);
          assertEquals("t0", columnNode.getTable());
          assertEquals("column", columnNode.getColumn());
      }
  }