add test for GroupByContextEngine (#3291)

* Add GroupByContextEngineTest

* Rename test variable

sharding-core/sharding-core-preprocessor/src/test/java/org/apache/shardingsphere/core/preprocessor/segment/select/groupby/engine/GroupByContextEngineTest.java

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.shardingsphere.core.preprocessor.segment.select.groupby.engine;
+
+import com.google.common.base.Optional;
+import org.apache.shardingsphere.core.parse.sql.segment.dml.order.GroupBySegment;
+import org.apache.shardingsphere.core.parse.sql.segment.dml.order.item.ColumnOrderByItemSegment;
+import org.apache.shardingsphere.core.parse.sql.segment.dml.order.item.IndexOrderByItemSegment;
+import org.apache.shardingsphere.core.parse.sql.statement.dml.SelectStatement;
+import org.apache.shardingsphere.core.preprocessor.segment.select.groupby.GroupByContext;
+import org.apache.shardingsphere.core.preprocessor.segment.select.orderby.OrderByItem;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public final class GroupByContextEngineTest {
+    
+    @Test
+    public void assertCreateGroupByContextWithoutGroupBy() {
+        SelectStatement selectStatement = mock(SelectStatement.class);
+        when(selectStatement.getGroupBy()).thenReturn(Optional.<GroupBySegment>absent());
+        GroupByContext actualGroupByContext = new GroupByContextEngine().createGroupByContext(selectStatement);
+        assertTrue(actualGroupByContext.getItems().isEmpty());
+        assertThat(actualGroupByContext.getLastIndex(), is(0));
+    }
+    
+    @Test
+    public void assertCreateGroupByContextWithGroupBy() {
+        SelectStatement selectStatement = mock(SelectStatement.class);
+        ColumnOrderByItemSegment columnOrderByItemSegment = mock(ColumnOrderByItemSegment.class);
+        IndexOrderByItemSegment indexOrderByItemSegment1 = mock(IndexOrderByItemSegment.class);
+        when(indexOrderByItemSegment1.getColumnIndex()).thenReturn(2);
+        IndexOrderByItemSegment indexOrderByItemSegment2 = mock(IndexOrderByItemSegment.class);
+        when(indexOrderByItemSegment2.getColumnIndex()).thenReturn(3);
+        GroupBySegment groupBySegment = mock(GroupBySegment.class);
+        when(groupBySegment.getGroupByItems()).thenReturn(Arrays.asList(columnOrderByItemSegment, indexOrderByItemSegment1, indexOrderByItemSegment2));
+        when(groupBySegment.getStopIndex()).thenReturn(10);
+        when(selectStatement.getGroupBy()).thenReturn(Optional.of(groupBySegment));
+        GroupByContext actualGroupByContext = new GroupByContextEngine().createGroupByContext(selectStatement);
+        OrderByItem orderByItem1 = new OrderByItem(indexOrderByItemSegment1);
+        orderByItem1.setIndex(2);
+        OrderByItem orderByItem2 = new OrderByItem(indexOrderByItemSegment2);
+        orderByItem2.setIndex(3);
+        assertThat(actualGroupByContext.getItems(), is((Collection<OrderByItem>) Arrays.asList(new OrderByItem(columnOrderByItemSegment), orderByItem1, orderByItem2)));
+        assertThat(actualGroupByContext.getLastIndex(), is(10));
+        List<OrderByItem> results = new ArrayList<>(actualGroupByContext.getItems());
+        assertThat(results.get(0).getIndex(), is(0));
+        assertThat(results.get(1).getIndex(), is(2));
+        assertThat(results.get(2).getIndex(), is(3));
+    }
+}