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   * 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.
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  package org.apache.beam.sdk.util.construction;
  
  import static org.hamcrest.MatcherAssert.assertThat;
  import static org.hamcrest.Matchers.equalTo;
  import static org.hamcrest.Matchers.not;
  
  import org.apache.beam.sdk.Pipeline.PipelineVisitor.Defaults;
  import org.apache.beam.sdk.runners.PTransformOverrideFactory.ReplacementOutput;
  import org.apache.beam.sdk.runners.TransformHierarchy;
  import org.apache.beam.sdk.testing.NeedsRunner;
  import org.apache.beam.sdk.testing.PAssert;
  import org.apache.beam.sdk.testing.TestPipeline;
  import org.apache.beam.sdk.transforms.Create;
  import org.apache.beam.sdk.transforms.Flatten;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.util.construction.DeduplicatedFlattenFactory.FlattenWithoutDuplicateInputs;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.PCollectionList;
  import org.apache.beam.sdk.values.PValues;
  import org.apache.beam.sdk.values.TaggedPValue;
  import org.hamcrest.Matchers;
  import org.junit.Rule;
  import org.junit.Test;
  import org.junit.experimental.categories.Category;
  import org.junit.runner.RunWith;
  import org.junit.runners.JUnit4;
  
  /** Tests for {@link DeduplicatedFlattenFactory}. */
  @RunWith(JUnit4.class)
  public class DeduplicatedFlattenFactoryTest {
    @Rule public TestPipeline pipeline = TestPipeline.create();
  
    private PCollection<String> first = pipeline.apply("FirstCreate", Create.of("one"));
    private PCollection<String> second = pipeline.apply("SecondCreate", Create.of("two"));
    private DeduplicatedFlattenFactory<String> factory = DeduplicatedFlattenFactory.create();
  
    @Test
    public void duplicatesInsertsMultipliers() {
      PTransform<PCollectionList<String>, PCollection<String>> replacement =
          new DeduplicatedFlattenFactory.FlattenWithoutDuplicateInputs<>();
      final PCollectionList<String> inputList =
          PCollectionList.of(first).and(second).and(first).and(first);
      inputList.apply(replacement);
      pipeline.traverseTopologically(
          new Defaults() {
            @Override
            public void visitPrimitiveTransform(TransformHierarchy.Node node) {
              if (node.getTransform() instanceof Flatten.PCollections) {
                assertThat(node.getInputs(), not(equalTo(inputList.expand())));
              }
            }
          });
    }
  
    @Test
    @Category(NeedsRunner.class)
    public void testOverride() {
      final PCollectionList<String> inputList =
          PCollectionList.of(first).and(second).and(first).and(first);
      PTransform<PCollectionList<String>, PCollection<String>> replacement =
          new FlattenWithoutDuplicateInputs<>();
      PCollection<String> flattened = inputList.apply(replacement);
  
      PAssert.that(flattened).containsInAnyOrder("one", "two", "one", "one");
      pipeline.run();
    }
  
    @Test
    public void outputMapping() {
      final PCollectionList<String> inputList =
          PCollectionList.of(first).and(second).and(first).and(first);
      PCollection<String> original = inputList.apply(Flatten.pCollections());
      PCollection<String> replacement = inputList.apply(new FlattenWithoutDuplicateInputs<>());
  
      assertThat(
          factory.mapOutputs(PValues.expandOutput(original), replacement),
          Matchers.hasEntry(
              replacement,
              ReplacementOutput.of(
                  TaggedPValue.ofExpandedValue(original),
                  TaggedPValue.ofExpandedValue(replacement))));
    }
  }
  