摘要：中常用的單元測(cè)試工具是老牌測(cè)試框架了，也是目前引用最廣泛的一個(gè)框架?？梢允褂眠m當(dāng)?shù)膯卧獪y(cè)試方式，比如可以提供一個(gè)測(cè)試接口，利用的熱部署功能實(shí)現(xiàn)不重啟及時(shí)修改代碼。

單元測(cè)試（英語(yǔ)：Unit Testing）又稱為模塊測(cè)試, 是針對(duì)程序模塊（軟件設(shè)計(jì)的最小單位）來(lái)進(jìn)行正確性檢驗(yàn)的測(cè)試工作。程序單元是應(yīng)用的最小可測(cè)試部件。在過(guò)程化編程中，一個(gè)單元就是單個(gè)程序、函數(shù)、過(guò)程等；對(duì)于面向?qū)ο缶幊?，最小單元就是方法，包括基類（超類）、抽象類、或者派生類（子類）中的方法?br>通常來(lái)說(shuō)，程序員每修改一次程序就會(huì)進(jìn)行最少一次單元測(cè)試，在編寫程序的過(guò)程中前后很可能要進(jìn)行多次單元測(cè)試，以證實(shí)程序達(dá)到軟件規(guī)格書要求的工作目標(biāo)，沒(méi)有程序錯(cuò)誤；雖然單元測(cè)試不是什么必須的，但也不壞，這牽涉到項(xiàng)目管理的政策決定。

優(yōu)質(zhì)的單元測(cè)試可以保障開(kāi)發(fā)質(zhì)量和程序的魯棒性。在大多數(shù)互聯(lián)網(wǎng)企業(yè)中開(kāi)發(fā)工程師在研發(fā)過(guò)程中都會(huì)頻繁地執(zhí)行測(cè)試用例，運(yùn)行失敗的單測(cè)能幫助我們快速排查和定位問(wèn)題 使問(wèn)題在被帶到線上之前完成修復(fù)。正如軟件工程界的一條金科玉律----越早發(fā)現(xiàn)的缺陷，其修復(fù)成本越低。一流的測(cè)試能發(fā)現(xiàn)未發(fā)生的故障；二流的測(cè)試能快速定位故障的發(fā)生點(diǎn)；三流的測(cè)試則疲于奔命，一直跟在故障后面進(jìn)行功能回歸。

https://junit.org/junit5/

junit是老牌測(cè)試框架了，也是目前引用最廣泛的一個(gè)框架。當(dāng)前已經(jīng)更新到Junit5，功能更強(qiáng)大。

class StandardTests {

    @BeforeAll
    static void initAll() {
    }

    @BeforeEach
    void init() {
    }

    @Test
    void succeedingTest() {
    }

    @Test
    void failingTest() {
        fail("a failing test");
    }

    @Test
    @Disabled("for demonstration purposes")
    void skippedTest() {
        // not executed
    }

    @Test
    void abortedTest() {
        assumeTrue("abc".contains("Z"));
        fail("test should have been aborted");
    }

    @AfterEach
    void tearDown() {
    }

    @AfterAll
    static void tearDownAll() {
    }

}

https://assertj.github.io/doc/

一個(gè)功能強(qiáng)悍的斷言工具，支持各種斷言方式

// entry point for all assertThat methods and utility methods (e.g. entry)
import static org.assertj.core.api.Assertions.*;

// basic assertions
assertThat(frodo.getName()).isEqualTo("Frodo");
assertThat(frodo).isNotEqualTo(sauron);

// chaining string specific assertions
assertThat(frodo.getName()).startsWith("Fro")
                           .endsWith("do")
                           .isEqualToIgnoringCase("frodo");

// collection specific assertions (there are plenty more)
// in the examples below fellowshipOfTheRing is a List
assertThat(fellowshipOfTheRing).hasSize(9)
                               .contains(frodo, sam)
                               .doesNotContain(sauron);

// as() is used to describe the test and will be shown before the error message
assertThat(frodo.getAge()).as("check %s"s age", frodo.getName()).isEqualTo(33);

// Java 8 exception assertion, standard style ...
assertThatThrownBy(() -> { throw new Exception("boom!"); }).hasMessage("boom!");
// ... or BDD style
Throwable thrown = catchThrowable(() -> { throw new Exception("boom!"); });
assertThat(thrown).hasMessageContaining("boom");

// using the "extracting" feature to check fellowshipOfTheRing character"s names (Java 7)
assertThat(fellowshipOfTheRing).extracting("name")
                               .contains("Boromir", "Gandalf", "Frodo", "Legolas")
// same thing using a Java 8 method reference
assertThat(fellowshipOfTheRing).extracting(TolkienCharacter::getName)
                               .doesNotContain("Sauron", "Elrond");

// extracting multiple values at once grouped in tuples (Java 7)
assertThat(fellowshipOfTheRing).extracting("name", "age", "race.name")
                               .contains(tuple("Boromir", 37, "Man"),
                                         tuple("Sam", 38, "Hobbit"),
                                         tuple("Legolas", 1000, "Elf"));

// filtering a collection before asserting in Java 7 ... 
assertThat(fellowshipOfTheRing).filteredOn("race", HOBBIT)
                               .containsOnly(sam, frodo, pippin, merry);
// ... or in Java 8
assertThat(fellowshipOfTheRing).filteredOn(character -> character.getName().contains("o"))
                               .containsOnly(aragorn, frodo, legolas, boromir);

// combining filtering and extraction (yes we can)
assertThat(fellowshipOfTheRing).filteredOn(character -> character.getName().contains("o"))
                               .containsOnly(aragorn, frodo, legolas, boromir)
                               .extracting(character -> character.getRace().getName())
                               .contains("Hobbit", "Elf", "Man");

// and many more assertions: iterable, stream, array, map, dates (java 7 and 8), path, file, numbers, predicate, optional ...

https://site.mockito.org/

一個(gè)單元測(cè)試中的Mock工具，可以很靈活的創(chuàng)建對(duì)象，配合單元測(cè)試。

// You can mock concrete classes and interfaces
TrainSeats seats = mock(TrainSeats.class);

// stubbing appears before the actual execution
when(seats.book(Seat.near(WINDOW).in(FIRST_CLASS))).thenReturn(BOOKED);

// the following prints "BOOKED"
System.out.println(seats.book(Seat.near(WINDOW).in(FIRST_CLASS)));

// the following prints "null" because 
// .book(Seat.near(AISLE).in(FIRST_CLASS))) was not stubbed
System.out.println(seats.book(Seat.near(AISLE).in(FIRST_CLASS)));

// the following verification passes because 
// .book(Seat.near(WINDOW).in(FIRST_CLASS)) has been invoked
verify(seats).book(Seat.near(WINDOW).in(FIRST_CLASS));

// the following verification fails because 
// .book(Seat.in(SECOND_CLASS)) has not been invoked
verify(seats).book(Seat.in(SECOND_CLASS));

對(duì)于業(yè)務(wù)代碼，有時(shí)單元測(cè)試并不方便，因?yàn)槊看螁?dòng)成本過(guò)高?？梢允褂眠m當(dāng)?shù)膯卧獪y(cè)試方式，比如可以提供一個(gè)測(cè)試接口，利用IDE的熱部署功能實(shí)現(xiàn)不重啟及時(shí)修改代碼。

但是對(duì)于非業(yè)務(wù)性代碼，進(jìn)行單元測(cè)試時(shí)非常有必要的，可以更早的發(fā)現(xiàn)代碼中的問(wèn)題，同時(shí)也可以檢驗(yàn)程序的解耦性。

良好的代碼設(shè)計(jì)在單元測(cè)試時(shí)會(huì)更方便，反之緊耦合的設(shè)計(jì)會(huì)給單元測(cè)試帶來(lái)很大的困擾。