Create bank account

Small first step to help drive the initial core of the domain project.

Extract micro types for the account id and the amount. The latter is
not currency specific but just minor units, which is pence for British
pounds.

Externalise account id generation to avoid having static references
in the class, which would have made the test more difficult to write.

Author: lmirabal

build.gradle

@@ -15,6 +15,7 @@ subprojects {
     dependencies {
         testImplementation 'org.jetbrains.kotlin:kotlin-test-junit5'
         testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
+        testImplementation 'com.natpryce:hamkrest:1.8.0.1'
         testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.0'
     }
 

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

@@ -0,0 +1,11 @@
+package lmirabal.bank
+
+import lmirabal.bank.model.Amount
+import lmirabal.bank.model.BankAccount
+import lmirabal.bank.model.BankAccountId
+
+class BankService(val idFactory: () -> BankAccountId = { BankAccountId.random() }) {
+    fun createAccount(): BankAccount {
+        return BankAccount(idFactory(), Amount.ZERO)
+    }
+}

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

@@ -0,0 +1,8 @@
+package lmirabal.bank.model
+
+data class Amount(val minorUnits: Long) {
+
+    companion object {
+        val ZERO = Amount(0)
+    }
+}

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

@@ -0,0 +1,12 @@
+package lmirabal.bank.model
+
+import java.util.UUID
+
+data class BankAccount(val id: BankAccountId, val balance: Amount)
+
+data class BankAccountId(val value: UUID) {
+
+    companion object {
+        fun random() = BankAccountId(UUID.randomUUID())
+    }
+}

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

@@ -0,0 +1,21 @@
+package lmirabal.bank
+
+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 BankServiceTest {
+    @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)))
+    }
+}