Hamcrest.md

介绍

Hamcrest是一个开源的库，07年被引入到Junit4。assertThat()是其中最常用的一个方法，位于org.junit.Assert包中, 方法签名如下:static <T> void assertThat(T actual, org.hamcrest.Matcher<T> matcher)。

使用方法

package com.edgibbs.junit.example;

import org.hamcrest.Description;
import org.hamcrest.Matcher;
import org.hamcrest.StringDescription;
import org.junit.Test;

import static org.hamcrest.CoreMatchers.*;
import static org.junit.Assert.assertThat;

public class HamcrestExamples {

  @Test
  public void allOfExampleShowsAllMatchersMustAllBeTrue() throws Exception {
    assertThat("Hello", is(allOf(notNullValue(), instanceOf(String.class), equalTo("Hello"))));
  }

  @Test
  public void allOfExampleShowsFailingIfOneMatcherDoesNotMatch() throws Exception {
    assertThat("Hello", is(not(allOf(notNullValue(), instanceOf(Integer.class)))));
  }

  @Test
  public void anyExampleChecksThatClassIsOfSameType() throws Exception {
    assertThat("Hello", is(any(String.class)));
  }

  @Test
  public void anyExampleShowsStringIsAlsoAnObject() throws Exception {
    assertThat("Hello", is(any(Object.class)));
  }

  @Test
  public void anyOfExampleReturnsTrueIfOneMatches() throws Exception {
    assertThat("Hello", is(anyOf(nullValue(), instanceOf(String.class), equalTo("Goodbye"))));
  }

  @Test
  public void anyOfExampleFailingIfAllMatchersAreFalse() throws Exception {
    assertThat("Hello", is(not(anyOf(nullValue(), instanceOf(Integer.class), equalTo("Goodbye")))));
  }

  @Test
  public void anythingExampleAlwaysReturnsTrue() throws Exception {
    assertThat("Hello", is(anything()));
  }

  // Feels very esoteric and not for typical usage used to override the description
  @Test
  public void describedAsExample() throws Exception {
    Matcher< ?> matcher = describedAs("My Description", anything());
    Description description = new StringDescription().appendDescriptionOf(matcher);
    assertThat("My Description", is(description.toString()));
  }

  @Test
  public void equalToExampleAddingTwoPlusTwo() throws Exception {
    assertThat(2 + 2, is(equalTo(4)));
  }

  @Test
  public void instanceOfExampleForString() throws Exception {
    assertThat("Hello", is(instanceOf(String.class)));
  }

  @Test
  public void isExampleShortCutForIsInstanceOfClass() throws Exception {
    assertThat("Hello", is(String.class));
    assertThat("Hello", instanceOf(String.class));
  }

  @Test
  public void isExampleShortCutAsJustSyntacticSugarUsedThreeTimes() throws Exception {
    assertThat("Hello", is(is(is(notNullValue()))));
  }

  @Test
  public void isExampleShortCutForIsEqualTo() throws Exception {
    assertThat("Hello", is("Hello"));
    assertThat("Hello", equalTo("Hello"));
  }

  @Test
  public void notExampleJustInvertsExpression() throws Exception {
    assertThat("Hello", is(not(instanceOf(Integer.class))));
  }

  @Test
  public void notNullValueExampleForString() throws Exception {
    assertThat("Hello", is(notNullValue()));
  }

  @Test
  public void notNullValueExampleForAClass() throws Exception {
    assertThat("Hello", is(notNullValue(Object.class)));
  }

  @Test
  public void nullValueExampleWithANull() throws Exception {
    assertThat(null, is(nullValue()));
  }

  @Test
  public void nullValueExampleWithANullType() throws Exception {
    Integer nothing = null;
    assertThat(nothing, is(nullValue(Integer.class)));
  }

  @Test
  public void sameInstanceExample() throws Exception {
    Object object = new Object();
    Object sameObject = object;
    assertThat(object, is(sameInstance(sameObject)));
  }

}