server/container/util/src/test/java/org/apache/james/util/StreamUtilsTest.java

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package org.apache.james.util;

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatThrownBy;

import java.util.stream.Stream;

import org.junit.jupiter.api.Test;

import com.google.common.collect.ImmutableList;

class StreamUtilsTest {

    @Test
    void flattenShouldReturnEmptyWhenEmptyStreams() {
        assertThat(
            StreamUtils.<Integer>flatten(ImmutableList.of())
                .collect(ImmutableList.toImmutableList()))
            .isEmpty();
    }

    @Test
    void flattenShouldPreserveSingleStreams() {
        assertThat(
            StreamUtils.flatten(ImmutableList.of(
                Stream.of(1, 2, 3)))
                .collect(ImmutableList.toImmutableList()))
            .containsExactly(1, 2, 3);
    }

    @Test
    void flattenShouldMergeSeveralStreamsTogether() {
        assertThat(
            StreamUtils.flatten(ImmutableList.of(
                Stream.of(1, 2, 3),
                Stream.of(4, 5)))
                .collect(ImmutableList.toImmutableList()))
            .containsExactly(1, 2, 3, 4, 5);
    }

    @Test
    void flattenShouldAcceptEmptyStreams() {
        assertThat(
            StreamUtils.flatten(ImmutableList.of(
                Stream.of()))
                .collect(ImmutableList.toImmutableList()))
            .isEmpty();
    }

    @Test
    void flattenShouldMergeEmptyStreamsWithOtherData() {
        assertThat(
            StreamUtils.flatten(ImmutableList.of(
                Stream.of(1, 2),
                Stream.of(),
                Stream.of(3)))
                .collect(ImmutableList.toImmutableList()))
            .containsExactly(1, 2, 3);
    }

    @Test
    void flattenShouldAcceptEmptyVarArg() {
        assertThat(
            StreamUtils.flatten()
                .collect(ImmutableList.toImmutableList()))
            .isEmpty();
    }

    @Test
    void flattenShouldThrowOnNullVarArg() {
        Stream<String>[] streams = null;
        assertThatThrownBy(() -> StreamUtils.flatten(streams).collect(ImmutableList.toImmutableList()))
            .isInstanceOf(NullPointerException.class);
    }

    @Test
    void flattenShouldFlattenNonEmptyVarArg() {
        assertThat(StreamUtils.flatten(Stream.of(1), Stream.of(2)).collect(ImmutableList.toImmutableList()))
            .containsExactly(1, 2);
    }

    @Test
    void ofNullableShouldReturnEmptyStreamWhenNull() {
        assertThat(StreamUtils.ofNullable(null)
            .collect(ImmutableList.toImmutableList()))
            .isEmpty();
    }

    @Test
    void ofNullableShouldReturnAStreamWithElementsOfTheArray() {
        assertThat(StreamUtils.ofNullable(ImmutableList.of(1, 2).toArray())
            .collect(ImmutableList.toImmutableList()))
            .containsExactly(1, 2);
    }
}