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Java 學習記錄107 — Introduction to Unit Testing with JUnit

張小雄
7 min readJan 18, 2022

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今天要學的是新篇章，測試功能

Tim老師教的是 Junit4，所以我練習也是用這版本

BankAccount.java

package bankAcoount;public class BankAccount {
    private String firstName;
    private String lastName;
    private double balance;    public BankAccount(String firstName, String lastName, double balance) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.balance = balance;
    }
    // The branch argument is true if the customer is performing the transaction
    // at  a branch, with a teller, otherwise is at an ATM
    public double deposit(double amount, boolean branch) {
        balance += amount;
        return balance;
    }    // The branch argument is true if the customer is performing the transaction
    // at  a branch, with a teller, otherwise is at an ATM
    public double withdraw(double amount, boolean branch) {
        balance -= amount;
        return balance;
    }    public double getBalance() {
        return balance;
    }    // More methods that use firstName, lastName, and perform other functions
}

接著對著 class name 點右下 More actions

點第一個 Create Test

本課學的是 Junit 4，還要記得把下面的 Member 都打勾

BankAccountTest.java

package bankAcoount;import org.junit.Test;import static org.junit.Assert.*;public class BankAccountTest {    @Test
    public void deposit() {
    }    @Test
    public void withdraw() {
    }    @Test
    public void getBalance() {
    }}

系統會新增一個 class，一開始都是空的

修改 BankAccountTest.java

package bankAcoount;import org.junit.Test;import static org.junit.Assert.*;public class BankAccountTest {    @Test
    public void deposit() {
        fail("Not yet implement");
    }    @Test
    public void withdraw() {
    }    @Test
    public void getBalance() {
    }    @Test
    public void dummyTest() {
        assertEquals(20, 50);
    }
}

接著右鍵點 Run

輸出結果：

第一個測試直接寫 fail 所以不會通過

最後一個測試寫，希望得到 20，但拿到的是 50，所以也沒通過

中間兩個測試都是空的，直接算通過

所以就是 2 個通過、2 個失敗

修改 BankAccountTest.java

@Test
public void deposit() {
    BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00);
    double balance = account.deposit(200.00, true);
    assertEquals(1200.00, balance, 0);
    assertEquals(1200.00, account.getBalance(), 0);}

測試結果：

通過

assertEquals()的參數分別為，希望得到的結果、實際給的數字，相差多少

不想一次運行所有測試可以只點行號旁邊的圖案，就可以單獨運行那個測試

修改 BankAccountTest.java

package bankAcoount;import org.junit.Test;import static org.junit.Assert.*;public class BankAccountTest {    @Test
    public void deposit() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00);
        double balance = account.deposit(200.00, true);
        assertEquals(1200.00, balance, 0);
    }    @Test
    public void withdraw() {
        fail("Not yet implement");
    }    @Test
    public void getBalance() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00);
        account.deposit(200.00, true);
        assertEquals(1200.00, account.getBalance(), 0);
    }}

測試結果：

通過，除了 withdraw()

主要是測試 getBalance()

Tim老師提醒說，所有的測試案例應該要可以分別單獨運行

所以 deposit() 也一起修改了

修改 BankAccountTest.java

package bankAcoount;import org.junit.Test;import static org.junit.Assert.*;public class BankAccountTest {    @Test
    public void deposit() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00);
        double balance = account.deposit(200.00, true);
        assertEquals(1200.00, balance, 0);
    }    @Test
    public void withdraw() {
        fail("Not yet implement");
    }    @Test
    public void getBalance_deposit() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00);
        account.deposit(200.00, true);
        assertEquals(1200.00, account.getBalance(), 0);
    }    @Test
    public void getBalance_withdraw() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00);
        account.withdraw(200.00, true);
        assertEquals(800.00, account.getBalance(), 0);
    }}

測試結果：

通過，除了 withdraw()

Tim老師又提醒說，測試名要有相關，就改成能直接看懂的名稱了

一個存款，一個提款，都符合希望得到的結果（1000 + 200＝1200，1000–200＝800）

BankAccount.java

package bankAcoount;public class BankAccount {
    private String firstName;
    private String lastName;
    private double balance;    public static final int CHECKING = 1;
    public static final int  SAVING = 1;    private int typeOfAccount;    public BankAccount(String firstName, String lastName, double balance, int typeOfAccount) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.balance = balance;
        this.typeOfAccount = typeOfAccount;
    }
    // The branch argument is true if the customer is performing the transaction
    // at  a branch, with a teller, otherwise is at an ATM
    public double deposit(double amount, boolean branch) {
        balance += amount;
        return balance;
    }    // The branch argument is true if the customer is performing the transaction
    // at  a branch, with a teller, otherwise is at an ATM
    public double withdraw(double amount, boolean branch) {
        balance -= amount;
        return balance;
    }    public double getBalance() {
        return balance;
    }    public boolean isChecking() {
        return typeOfAccount == CHECKING;
    }    // More methods that use firstName, lastName, and perform other functions
}

修改 BankAccountTest.java

package bankAcoount;import org.junit.Test;import static org.junit.Assert.*;public class BankAccountTest {    @Test
    public void deposit() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.CHECKING);
        double balance = account.deposit(200.00, true);
        assertEquals(1200.00, balance, 0);
    }    @Test
    public void withdraw() {
        fail("Not yet implement");
    }    @Test
    public void getBalance_deposit() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.CHECKING);
        account.deposit(200.00, true);
        assertEquals(1200.00, account.getBalance(), 0);
    }    @Test
    public void getBalance_withdraw() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.CHECKING);
        account.withdraw(200.00, true);
        assertEquals(800.00, account.getBalance(), 0);
    }    @Test
    public void isChecking_true() {
        BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.CHECKING);
        assertTrue(account.isChecking());
    }}

測試結果：

通過，除了 withdraw()

新增一個測試，帳戶類型是否為支票戶

修改 BankAccountTest.java

@Test
public void isChecking_true() {
    BankAccount account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.SAVING);
    assertTrue("The account is NOT a checking account", account.isChecking());
}

測試結果：

java.lang.AssertionError: The account is NOT a checking account

at org.junit.Assert.fail(Assert.java:89)

at org.junit.Assert.assertTrue(Assert.java:42)

at bankAcoount.BankAccountTest.isChecking_true(BankAccountTest.java:38)

（以下省略）

改成存戶，測試就沒通過，還可自訂錯誤提示

修改 BankAccountTest.java

package bankAcoount;import org.junit.Before;
import org.junit.Test;import static org.junit.Assert.*;public class BankAccountTest {    private BankAccount account;    @Before
    public void setup() {
        account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.CHECKING);
        System.out.println("Running a test...");
    }    @Test
    public void deposit() {
        double balance = account.deposit(200.00, true);
        assertEquals(1200.00, balance, 0);
    }    @Test
    public void withdraw() {
        fail("Not yet implement");
    }    @Test
    public void getBalance_deposit() {
        account.deposit(200.00, true);
        assertEquals(1200.00, account.getBalance(), 0);
    }    @Test
    public void getBalance_withdraw() {
        account.withdraw(200.00, true);
        assertEquals(800.00, account.getBalance(), 0);
    }    @Test
    public void isChecking_true() {
        assertTrue("The account is NOT a checking account", account.isChecking());
    }}

測試結果：

Running a test…

java.lang.AssertionError: Not yet implement

at org.junit.Assert.fail(Assert.java:89)

at bankAcoount.BankAccountTest.withdraw(BankAccountTest.java:26)

（省略部份）

Running a test…

Running a test…

Running a test…

Running a test…

把之前測試都會使用的部份，抽出來放到 setup() 裡面

跑每個測試的時候，都會運行一次

修改 BankAccountTest.java

package bankAcoount;import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;import static org.junit.Assert.*;public class BankAccountTest {    private BankAccount account;    @BeforeClass
    public static void beforeClass(){
        System.out.println("This executes before any test cases");
    }    @Before
    public void setup() {
        account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.CHECKING);
        System.out.println("Running a test...");
    }    @Test
    public void deposit() {
        double balance = account.deposit(200.00, true);
        assertEquals(1200.00, balance, 0);
    }    @Test
    public void withdraw() {
        fail("Not yet implement");
    }    @Test
    public void getBalance_deposit() {
        account.deposit(200.00, true);
        assertEquals(1200.00, account.getBalance(), 0);
    }    @Test
    public void getBalance_withdraw() {
        account.withdraw(200.00, true);
        assertEquals(800.00, account.getBalance(), 0);
    }    @Test
    public void isChecking_true() {
        assertTrue("The account is NOT a checking account", account.isChecking());
    }    @AfterClass
    public static void afterClass(){
        System.out.println("This executes after any test cases.");
    }}

測試結果：

This executes before any test cases

Running a test…

java.lang.AssertionError: Not yet implement

at org.junit.Assert.fail(Assert.java:89)

at bankAcoount.BankAccountTest.withdraw(BankAccountTest.java:33)

（省略部份）

Running a test…

Running a test…

Running a test…

Running a test…

若不想每一次都執行，只想在測試案例之前或之後執行一次就好，則可以使用 @BeforeClass 跟 @AfterClass

Tim 老師提醒說，若是在測試結果中，This executes before any test cases 這句若跑到下面，並不代表執行順序就是那樣

修改 BankAccountTest.java

package bankAcoount;import org.junit.*;import static org.junit.Assert.*;public class BankAccountTest {    private BankAccount account;
    private static int count;    @BeforeClass
    public static void beforeClass(){
        System.out.println("This executes before any test cases. Count = " + count++);
    }    @Before
    public void setup() {
        account = new BankAccount("Tim", "Jimmy", 1000.00, BankAccount.CHECKING);
        System.out.println("Running a test...");
    }    @Test
    public void deposit() {
        double balance = account.deposit(200.00, true);
        assertEquals(1200.00, balance, 0);
    }    @Test
    public void withdraw() {
        fail("Not yet implement");
    }    @Test
    public void getBalance_deposit() {
        account.deposit(200.00, true);
        assertEquals(1200.00, account.getBalance(), 0);
    }    @Test
    public void getBalance_withdraw() {
        account.withdraw(200.00, true);
        assertEquals(800.00, account.getBalance(), 0);
    }    @Test
    public void isChecking_true() {
        assertTrue("The account is NOT a checking account", account.isChecking());
    }    @After
    public void teardown(){
        System.out.println("Count = " + count++);
    }    @AfterClass
    public static void afterClass(){
        System.out.println("This executes after any test cases. Count = " + count++);
    }}

測試結果：

This executes before any test cases. Count = 0

Running a test…

Count = 1

java.lang.AssertionError: Not yet implement

at org.junit.Assert.fail(Assert.java:89)

at bankAcoount.BankAccountTest.withdraw(BankAccountTest.java:31)

Running a test…

Count = 2

Running a test…

Count = 3

Running a test…

Count = 4

Running a test…

Count = 5

This executes after any test cases. Count = 6

新增了一個 @After，每個測試案例都會執行一次

還加入了計數器，看著數字變化就能知道執行的順序為何

好處是就算測試結果的順序顯示亂掉了，也能從計數器看出順序

修改 BankAccount.java

// The branch argument is true if the customer is performing the transaction
// at  a branch, with a teller, otherwise is at an ATM
public double withdraw(double amount, boolean branch) {
    if ((amount > 500.00) && !branch) {
        throw new IllegalArgumentException();
    }
    balance -= amount;
    return balance;
}

修改 BankAccountTest.java

@Test
public void withdraw() {
    double balance = account.withdraw(600.00, true);
    assertEquals(400.00, balance, 0);
}

測試結果：

全通過

修改了 withdraw() 跟測試案例

若從 ATM 提款大於 500 元就會報錯

修改 BankAccountTest.java

@Test
public void withdraw_branch() {
    double balance = account.withdraw(600.00, true);
    assertEquals(400.00, balance, 0);
}@Test
public void withdraw_notBranch() {
    double balance = account.withdraw(600.00, false);
    assertEquals(400.00, balance, 0);
}

測試結果：

This executes before any test cases. Count = 0

Running a test…

Count = 1

java.lang.IllegalArgumentException

at bankAcoount.BankAccount.withdraw(BankAccount.java:32)

at bankAcoount.BankAccountTest.withdraw_notBranch(BankAccountTest.java:37)

Running a test…

Count = 2

Running a test…

Count = 3

Running a test…

Count = 4

Running a test…

Count = 5

Running a test…

Count = 6

This executes after any test cases. Count = 7

拆成兩隻測試

跟我們預期的一樣，第二次測試沒有通過

但我們這邊本來就是設計成能拋錯，代表有通過才是

不應該歸類在沒通過

修改 BankAccountTest.java

@Test(expected = IllegalArgumentException.class)
public void withdraw_notBranch() {
    double balance = account.withdraw(600.00, false);
    assertEquals(400.00, balance, 0);
}

測試結果：

全通過

修改的方法，在 @Test 旁邊加上參數即可

若照我們預期拋出來這個錯誤，那代表測試成功

@Test
public void withdraw_branch() {
    account.withdraw(600.00, true);
}@Test(expected = IllegalArgumentException.class)
public void withdraw_notBranch() {
    account.withdraw(600.00, false);
}

其實 asserEquals() 在這裡沒用到，直接移除也行

不會影響到運行結果

@Test //(expected = IllegalArgumentException.class)
public void withdraw_notBranch() {
    try {
        account.withdraw(600.00, false);
    } catch (IllegalArgumentException ignored) {
        
    }
}

注意 @Test 後面註釋掉了

這種寫法是 Junit4 之前的寫法

@Test //(expected = IllegalArgumentException.class)
public void withdraw_notBranch() {
    try {
        account.withdraw(600.00, true);
        fail("Should have thrown and IllegalArgumentException");
    } catch (IllegalArgumentException ignored) {    }
}

測試結果：

This executes before any test cases. Count = 0

Running a test…

Count = 1

java.lang.AssertionError: Should have thrown and IllegalArgumentException

at org.junit.Assert.fail(Assert.java:89)

at bankAcoount.BankAccountTest.withdraw_notBranch(BankAccountTest.java:38)

This executes after any test cases. Count = 2

加上自訂錯誤提示，就這樣寫

上面代碼全都紀錄在我的 Github

Java
Programming
Learning
Coding
Taiwan

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張小雄
張小雄

Written by 張小雄

35 Followers
19 Following

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