List bank accounts persisted in repository

Add the first port, a driven one, which allows to persist accounts.

The domain should only provide the contract definition of how it
interacts with the repository and the decision on how the mechanism is
going to work in the production system is delayed without interrupting
development. However, an in-memory implementation is available for test
purposes so that mocking is not necessary.

Author: lmirabal

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

@@ -1,11 +1,18 @@
 package lmirabal.bank
 
+import lmirabal.bank.data.BankAccountRepository
 import lmirabal.bank.model.Amount
 import lmirabal.bank.model.BankAccount
 import lmirabal.bank.model.BankAccountId
 
-class BankService(val idFactory: () -> BankAccountId = { BankAccountId.random() }) {
+class BankService(
+    private val accountRepository: BankAccountRepository,
+    private val idFactory: () -> BankAccountId = { BankAccountId.random() }
+) {
     fun createAccount(): BankAccount {
         return BankAccount(idFactory(), Amount.ZERO)
+            .also { newAccount -> accountRepository.add(newAccount) }
     }
+
+    fun listAccounts(): List<BankAccount> = accountRepository.list()
 }

domain/src/main/kotlin/lmirabal/bank/data/BankAccountRepository.kt

@@ -0,0 +1,8 @@
+package lmirabal.bank.data
+
+import lmirabal.bank.model.BankAccount
+
+interface BankAccountRepository {
+    fun add(account: BankAccount)
+    fun list(): List<BankAccount>
+}

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

@@ -2,20 +2,31 @@ package lmirabal.bank
 
 import com.natpryce.hamkrest.assertion.assertThat
 import com.natpryce.hamkrest.equalTo
+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.Test
 
 class BankServiceTest {
+    private val id = BankAccountId.random()
+    private val idFactory = { id }
+    private val bank = BankService(InMemoryBankAccountRepository(), idFactory)
+
     @Test
     fun createsAnAccount() {
-        val id = BankAccountId.random()
-        val idFactory = { id }
-        val bank = BankService(idFactory)
-
         val account = bank.createAccount()
 
         assertThat(account, equalTo(BankAccount(id, Amount.ZERO)))
     }
+
+    @Test
+    fun listsAccounts() {
+        val account1 = bank.createAccount()
+        val account2 = bank.createAccount()
+
+        val accounts = bank.listAccounts()
+
+        assertThat(accounts, equalTo(listOf(account1, account2)))
+    }
 }

domain/src/test/kotlin/lmirabal/bank/data/InMemoryBankAccountRepository.kt

@@ -0,0 +1,13 @@
+package lmirabal.bank.data
+
+import lmirabal.bank.model.BankAccount
+
+class InMemoryBankAccountRepository : BankAccountRepository {
+    private val accounts: MutableList<BankAccount> = arrayListOf()
+
+    override fun add(account: BankAccount) {
+        accounts.add(account)
+    }
+
+    override fun list(): List<BankAccount> = accounts
+}

domain/src/test/kotlin/lmirabal/bank/data/InMemoryBankAccountRepositoryTest.kt

@@ -0,0 +1,22 @@
+package lmirabal.bank.data
+
+import com.natpryce.hamkrest.assertion.assertThat
+import com.natpryce.hamkrest.equalTo
+import lmirabal.bank.model.Amount
+import lmirabal.bank.model.BankAccount
+import lmirabal.bank.model.BankAccountId
+import org.junit.jupiter.api.Test
+
+class InMemoryBankAccountRepositoryTest {
+    private val repository = InMemoryBankAccountRepository()
+
+    @Test
+    fun persistsAccounts() {
+        val account1 = BankAccount(BankAccountId.random(), Amount(10))
+        repository.add(account1)
+        val account2 = BankAccount(BankAccountId.random(), Amount(20))
+        repository.add(account2)
+
+        assertThat(repository.list(), equalTo(listOf(account1, account2)))
+    }
+}