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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
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  package org.apache.beam.examples.cookbook;
  
  import java.util.Arrays;
  import java.util.List;
  import org.apache.beam.sdk.coders.StringUtf8Coder;
  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.Distinct;
  import org.apache.beam.sdk.values.PCollection;
  import org.junit.Rule;
  import org.junit.Test;
  import org.junit.runner.RunWith;
  import org.junit.runners.JUnit4;
  
  /** Unit tests for {@link Distinct}. */
  @RunWith(JUnit4.class)
  public class DistinctExampleTest {
  
    @Rule public TestPipeline p = TestPipeline.create();
  
    @Test
    public void testDistinct() {
      List<String> strings = Arrays.asList("k1", "k5", "k5", "k2", "k1", "k2", "k3");
  
      PCollection<String> input = p.apply(Create.of(strings).withCoder(StringUtf8Coder.of()));
  
      PCollection<String> output = input.apply(Distinct.create());
  
      PAssert.that(output).containsInAnyOrder("k1", "k5", "k2", "k3");
      p.run().waitUntilFinish();
    }
  
    @Test
    public void testDistinctEmpty() {
      List<String> strings = Arrays.asList();
  
      PCollection<String> input = p.apply(Create.of(strings).withCoder(StringUtf8Coder.of()));
  
      PCollection<String> output = input.apply(Distinct.create());
  
      PAssert.that(output).empty();
      p.run().waitUntilFinish();
    }
  }
  