update TransactionService with withdrawal

src/main/kotlin/ltd/lulz/service/TransactionService.kt

@@ -2,7 +2,9 @@ package ltd.lulz.service
 
 import io.github.oshai.kotlinlogging.KotlinLogging
 import java.math.BigDecimal
+import java.math.BigDecimal.ZERO
 import java.util.UUID
+import ltd.lulz.exception.InsufficientFundsException
 import ltd.lulz.model.AccountEntity
 import org.springframework.stereotype.Service
 import org.springframework.transaction.annotation.Transactional
@@ -23,4 +25,15 @@ class TransactionService(
         .map { it.copy(amount = it.amount + amount) }
         .doOnNext { log.trace { "Deposited $amount to account ${it.id}" } }
         .flatMap { accountService.save(it) }
+
+    @Transactional
+    fun withdrawal(
+        account: UUID,
+        amount: BigDecimal,
+    ): Mono<AccountEntity> = accountService.getForUpdateById(account)
+        .map { it.copy(amount = it.amount - amount) }
+        .filter { it.amount >= ZERO }
+        .doOnNext { log.trace { "withdrawal $amount to account ${it.id}" } }
+        .switchIfEmpty(Mono.error(InsufficientFundsException()))
+        .flatMap { accountService.save(it) }
 }

src/test/kotlin/ltd/lulz/service/TransactionServiceTest.kt

@@ -7,9 +7,11 @@ import io.mockk.verify
 import java.math.BigDecimal
 import java.util.UUID
 import ltd.lulz.exception.AccountNotFoundException
+import ltd.lulz.exception.InsufficientFundsException
 import ltd.lulz.model.AccountEntity
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Nested
 import org.junit.jupiter.api.Test
 import reactor.core.publisher.Mono
 import reactor.test.StepVerifier
@@ -31,6 +33,9 @@ class TransactionServiceTest {
         service = TransactionService(accountService)
     }
 
+    @Nested
+    inner class Deposit {
+
         @Test
         fun `deposit to account - success`() {
             // given
@@ -71,4 +76,68 @@ class TransactionServiceTest {
             verify(exactly = 1) { accountService.getForUpdateById(any(UUID::class)) }
             verify(exactly = 0) { accountService.save(any()) }
         }
+    }
+
+    @Nested
+    inner class Withdrawal {
+
+        @Test
+        fun `withdrawal from account - success`() {
+            // given
+            val deposit = BigDecimal.valueOf(1.01)
+
+            val capture = slot<UUID>()
+            every { accountService.getForUpdateById(capture(capture)) }
+                .answers { Mono.just(AccountEntity(capture.captured, name, amount)) }
+            val entity = slot<AccountEntity>()
+            every { accountService.save(capture(entity)) }
+                .answers { Mono.just(entity.captured) }
+
+            // when stepped
+            StepVerifier.create(service.withdrawal(uuid, deposit))
+                .assertNext { result ->
+                    assertThat(result.id).isEqualTo(uuid)
+                    assertThat(result.name).isEqualTo(name)
+                    assertThat(result.amount).isEqualTo(amount - deposit)
+                }
+                .verifyComplete()
+
+            verify(exactly = 1) { accountService.getForUpdateById(any(UUID::class)) }
+            verify(exactly = 1) { accountService.save(any()) }
+        }
+
+        @Test
+        fun `withdrawal from account - insufficient founds`() {
+            // given
+            val deposit = BigDecimal.valueOf(1.10)
+
+            val capture = slot<UUID>()
+            every { accountService.getForUpdateById(capture(capture)) }
+                .answers { Mono.just(AccountEntity(capture.captured, name, amount)) }
+
+            // when stepped
+            StepVerifier.create(service.withdrawal(uuid, deposit))
+                .expectError(InsufficientFundsException::class.java)
+                .verify()
+
+            verify(exactly = 1) { accountService.getForUpdateById(any(UUID::class)) }
+            verify(exactly = 0) { accountService.save(any()) }
+        }
+
+        @Test
+        fun `withdrawal from account - account not found`() {
+            // given
+            val deposit = BigDecimal.valueOf(1.10)
+
+            every { accountService.getForUpdateById(any()) } returns Mono.error(AccountNotFoundException())
+
+            // when stepped
+            StepVerifier.create(service.withdrawal(uuid, deposit))
+                .expectError(AccountNotFoundException::class.java)
+                .verify()
+
+            verify(exactly = 1) { accountService.getForUpdateById(any(UUID::class)) }
+            verify(exactly = 0) { accountService.save(any()) }
+        }
+    }
 }