WeightedSnapshotTest.java

package io.dropwizard.metrics;

import org.junit.Test;

import io.dropwizard.metrics.Snapshot;
import io.dropwizard.metrics.WeightedSnapshot;
import io.dropwizard.metrics.WeightedSnapshot.WeightedSample;

import java.io.ByteArrayOutputStream;
import java.util.ArrayList;
import java.util.List;

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.offset;
import static org.mockito.Mockito.spy;
import static org.mockito.Mockito.when;

public class WeightedSnapshotTest {
    
    static public ArrayList<WeightedSample> WeightedArray(long[] values, double[] weights) {
        if (values.length != weights.length) {
            throw new IllegalArgumentException("Mismatched lengths: " + values.length + " vs " + weights.length);
        }
        
        final ArrayList<WeightedSample> samples = new ArrayList<>();
        for (int i = 0; i < values.length; i++) {
            samples.add(new WeightedSnapshot.WeightedSample(values[i], weights[i]));
        }
        
        return samples;
    }
    
    private final Snapshot snapshot = new WeightedSnapshot(
            WeightedArray(new long[]{5, 1, 2, 3, 4}, new double[]{1, 2, 3, 2, 2}) );

    @Test
    public void smallQuantilesAreTheFirstValue() throws Exception {
        assertThat(snapshot.getValue(0.0))
                .isEqualTo(1.0, offset(0.1));
    }

    @Test
    public void bigQuantilesAreTheLastValue() throws Exception {
        assertThat(snapshot.getValue(1.0))
                .isEqualTo(5.0, offset(0.1));
    }

    @Test(expected = IllegalArgumentException.class)
    public void disallowsNotANumberQuantile() {
        snapshot.getValue( Double.NaN );
    }

    @Test(expected = IllegalArgumentException.class)
    public void disallowsNegativeQuantile() {
        snapshot.getValue( -0.5 );
    }

    @Test(expected = IllegalArgumentException.class)
    public void disallowsQuantileOverOne() {
        snapshot.getValue( 1.5 );
    }

    @Test
    public void hasAMedian() throws Exception {
        assertThat(snapshot.getMedian()).isEqualTo(3.0, offset(0.1));
    }

    @Test
    public void hasAp75() throws Exception {
        assertThat(snapshot.get75thPercentile()).isEqualTo(4.0, offset(0.1));
    }

    @Test
    public void hasAp95() throws Exception {
        assertThat(snapshot.get95thPercentile()).isEqualTo(5.0, offset(0.1));
    }

    @Test
    public void hasAp98() throws Exception {
        assertThat(snapshot.get98thPercentile()).isEqualTo(5.0, offset(0.1));
    }

    @Test
    public void hasAp99() throws Exception {
        assertThat(snapshot.get99thPercentile()).isEqualTo(5.0, offset(0.1));
    }

    @Test
    public void hasAp999() throws Exception {
        assertThat(snapshot.get999thPercentile()).isEqualTo(5.0, offset(0.1));
    }

    @Test
    public void hasValues() throws Exception {
        assertThat(snapshot.getValues())
                .containsOnly(1, 2, 3, 4, 5);
    }

    @Test
    public void hasASize() throws Exception {
        assertThat(snapshot.size())
                .isEqualTo(5);
    }

    @Test
    public void worksWithUnderestimatedCollections() throws Exception {
        final List<WeightedSample> items = spy(WeightedArray(new long[]{5, 1, 2, 3, 4}, new double[]{1, 2, 3, 2, 2}));
        when(items.size()).thenReturn(4, 5);

        final Snapshot other = new WeightedSnapshot(items);

        assertThat(other.getValues())
                .containsOnly(1, 2, 3, 4, 5);
    }

    @Test
    public void worksWithOverestimatedCollections() throws Exception {
        final List<WeightedSample> items = spy(WeightedArray(new long[]{5, 1, 2, 3, 4}, new double[]{1, 2, 3, 2, 2}));
        when(items.size()).thenReturn(6, 5);

        final Snapshot other = new WeightedSnapshot(items);

        assertThat(other.getValues())
                .containsOnly(1, 2, 3, 4, 5);
    }

    @Test
    public void dumpsToAStream() throws Exception {
        final ByteArrayOutputStream output = new ByteArrayOutputStream();

        snapshot.dump(output);

        assertThat(output.toString())
                .isEqualTo(String.format("1%n2%n3%n4%n5%n"));
    }

    @Test
    public void calculatesTheMinimumValue() throws Exception {
        assertThat(snapshot.getMin())
                .isEqualTo(1);
    }

    @Test
    public void calculatesTheMaximumValue() throws Exception {
        assertThat(snapshot.getMax())
                .isEqualTo(5);
    }

    @Test
    public void calculatesTheMeanValue() throws Exception {
        assertThat(snapshot.getMean())
                .isEqualTo(2.7);
    }

    @Test
    public void calculatesTheStdDev() throws Exception {
        assertThat(snapshot.getStdDev())
                .isEqualTo(1.2688, offset(0.0001));
    }

    @Test
    public void calculatesAMinOfZeroForAnEmptySnapshot() throws Exception {
        final Snapshot emptySnapshot = new WeightedSnapshot(
            WeightedArray(new long[]{}, new double[]{}) );

        assertThat(emptySnapshot.getMin())
                .isZero();
    }

    @Test
    public void calculatesAMaxOfZeroForAnEmptySnapshot() throws Exception {
        final Snapshot emptySnapshot = new WeightedSnapshot(
            WeightedArray(new long[]{}, new double[]{}) );

        assertThat(emptySnapshot.getMax())
                .isZero();
    }

    @Test
    public void calculatesAMeanOfZeroForAnEmptySnapshot() throws Exception {
        final Snapshot emptySnapshot = new WeightedSnapshot(
            WeightedArray(new long[]{}, new double[]{}) );

        assertThat(emptySnapshot.getMean())
                .isZero();
    }

    @Test
    public void calculatesAStdDevOfZeroForAnEmptySnapshot() throws Exception {
        final Snapshot emptySnapshot = new WeightedSnapshot(
            WeightedArray(new long[]{}, new double[]{}) );

        assertThat(emptySnapshot.getStdDev())
                .isZero();
    }

    @Test
    public void calculatesAStdDevOfZeroForASingletonSnapshot() throws Exception {
        final Snapshot singleItemSnapshot = new WeightedSnapshot(
            WeightedArray(new long[]{ 1 }, new double[]{ 1.0 }) );

        assertThat(singleItemSnapshot.getStdDev())
                .isZero();
    }

    @Test
    public void expectNoOverflowForLowWeights() throws Exception {
        final Snapshot scatteredSnapshot = new WeightedSnapshot(
            WeightedArray(
                    new long[]{ 1, 2, 3 }, 
                    new double[]{ Double.MIN_VALUE, Double.MIN_VALUE, Double.MIN_VALUE }
            ) 
        );

        assertThat(scatteredSnapshot.getMean())
                .isEqualTo(2);
    }

}