Implement funds withdrawals in the domain

Make sure only the domain functional test is run using junit5 tags for
conditional execution.

Author: lmirabal

domain/src/main/kotlin/lmirabal/bank/Bank.kt

@@ -8,4 +8,5 @@ interface Bank {
     fun createAccount(): BankAccount
     fun listAccounts(): List<BankAccount>
     fun deposit(id: BankAccountId, amount: Amount): BankAccount
+    fun withdraw(id: BankAccountId, amount: Amount): BankAccount
 }

domain/src/main/kotlin/lmirabal/bank/BankService.kt

@@ -21,4 +21,10 @@ class BankService(
         return account.deposit(amount)
             .also { updatedAccount -> accountRepository.update(updatedAccount) }
     }
+
+    override fun withdraw(id: BankAccountId, amount: Amount): BankAccount {
+        val account = accountRepository.list().first { it.id == id }
+        return account.withdraw(amount)
+            .also { updatedAccount -> accountRepository.update(updatedAccount) }
+    }
 }

domain/src/main/kotlin/lmirabal/bank/model/Amount.kt

@@ -9,6 +9,10 @@ data class Amount(val minorUnits: Long) {
         return Amount(minorUnits + other.minorUnits)
     }
 
+    operator fun minus(other: Amount): Amount {
+        return Amount(minorUnits - other.minorUnits)
+    }
+
     companion object {
         val ZERO = Amount(0)
     }

domain/src/main/kotlin/lmirabal/bank/model/BankAccount.kt

@@ -6,6 +6,10 @@ data class BankAccount(val id: BankAccountId, val balance: Amount) {
     fun deposit(amount: Amount): BankAccount {
         return copy(balance = balance + amount)
     }
+
+    fun withdraw(amount: Amount): BankAccount {
+        return copy(balance = balance - amount)
+    }
 }
 
 data class BankAccountId(val value: UUID) {

domain/src/test/kotlin/lmirabal/bank/BankServiceTest.kt

@@ -6,8 +6,10 @@ import lmirabal.bank.data.InMemoryBankAccountRepository
 import lmirabal.bank.model.Amount
 import lmirabal.bank.model.BankAccount
 import lmirabal.bank.model.BankAccountId
+import org.junit.jupiter.api.Tag
 import org.junit.jupiter.api.Test
 
+@Tag("ImplementationReady")
 class BankServiceTest : BankTest() {
     private val idFactory = RecordingIdFactory()
     override val bank = BankService(InMemoryBankAccountRepository(), idFactory)

domain/src/test/kotlin/lmirabal/bank/model/AmountTest.kt

@@ -17,4 +17,11 @@ class AmountTest {
 
         assertThat(result, equalTo(Amount(40)))
     }
+
+    @Test
+    fun subtracts() {
+        val result = Amount(30) - Amount(10)
+
+        assertThat(result, equalTo(Amount(20)))
+    }
 }

domain/src/test/kotlin/lmirabal/bank/model/BankAccountTest.kt

@@ -14,4 +14,14 @@ class BankAccountTest {
 
         assertThat(updatedAccount, equalTo(BankAccount(id, Amount(300))))
     }
+
+    @Test
+    fun `decreases balance on withdrawal`() {
+        val id = BankAccountId.random()
+        val account = BankAccount(id, Amount(300))
+
+        val updatedAccount = account.withdraw(Amount(200))
+
+        assertThat(updatedAccount, equalTo(BankAccount(id, Amount(100))))
+    }
 }

domain/src/testFixtures/kotlin/lmirabal/bank/BankTest.kt

@@ -4,6 +4,8 @@ import com.natpryce.hamkrest.assertion.assertThat
 import com.natpryce.hamkrest.equalTo
 import lmirabal.bank.model.Amount
 import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.condition.EnabledIf
+import org.junit.jupiter.api.extension.ExtensionContext
 
 abstract class BankTest {
     abstract val bank: Bank
@@ -27,4 +29,17 @@ abstract class BankTest {
 
         assertThat(updatedAccount.balance, equalTo(Amount(300)))
     }
+
+    @EnabledIf("implementationReady")
+    @Test
+    fun `withdraws from account`() {
+        val bankAccount = bank.createAccount()
+
+        bank.deposit(bankAccount.id, Amount(300))
+        val updatedAccount = bank.withdraw(bankAccount.id, Amount(200))
+
+        assertThat(updatedAccount.balance, equalTo(Amount(100)))
+    }
+
+    fun implementationReady(context: ExtensionContext) = "ImplementationReady" in context.tags
 }

http/src/main/kotlin/lmirabal/bank/http/BankHttpClient.kt

@@ -28,4 +28,8 @@ class BankHttpClient(val http: HttpHandler) : Bank {
         )
         return bankAccountLens(response)
     }
+
+    override fun withdraw(id: BankAccountId, amount: Amount): BankAccount {
+        TODO("Not yet implemented")
+    }
 }

web/src/test/kotlin/lmirabal/bank/web/BankWebTest.kt

@@ -61,6 +61,10 @@ class BankWebDriver(web: HttpHandler) : Bank {
         return driver.getBankAccounts().first { account -> account.id == id }
     }
 
+    override fun withdraw(id: BankAccountId, amount: Amount): BankAccount {
+        TODO("Not yet implemented")
+    }
+
     private fun WebElement.getBankAccountId(): BankAccountId {
         val idText = getTableColumn(ID_INDEX)
         return BankAccountId(UUID.fromString(idText))