Refactored tests, added custom exceptions.

src/main/kotlin/camilyed/github/io/common/Money.kt

@@ -7,7 +7,9 @@ data class Money(val amount: BigDecimal, val currency: String) {
 
     init {
         require(amount >= BigDecimal.ZERO) { "Money amount must be greater than or equal to zero" }
-        require(currency.isNotEmpty()) { "Currency cannot be empty" }
+        require(currency == "PLN" || currency == "USD") {
+            throw UnsupportedCurrencyException("Unsupported currency: $currency")
+        }
         amount.setScale(2, RoundingMode.HALF_EVEN)
     }
 
@@ -36,3 +38,4 @@ data class Money(val amount: BigDecimal, val currency: String) {
         fun usd(amount: BigDecimal) = Money(amount.setScale(2, RoundingMode.HALF_EVEN), "USD")
     }
 }
+class UnsupportedCurrencyException(message: String) : RuntimeException(message)

src/main/kotlin/camilyed/github/io/currencyexchangeapi/domain/Account.kt

@@ -17,18 +17,18 @@ class Account(
     }
 
     fun exchangePlnToUsd(amountPln: Money, exchangeRate: ExchangeRate) {
-        require(amountPln.currency == "PLN") { "Amount must be in PLN" }
-        require(!amountPln.isZero()) { "Amount must be greater than 0" }
-        require(amountPln <= balancePln) { "Insufficient PLN balance" }
+        require(!amountPln.isZero()) { throw InvalidAmountException("Amount must be greater than 0") }
+        require(amountPln <= balancePln) { throw InsufficientFundsException("Insufficient PLN balance") }
+
         val amountUsd = Money(exchangeRate.convertFromPln(amountPln.amount), "USD")
         balancePln -= amountPln
         balanceUsd += amountUsd
     }
 
     fun exchangeUsdToPln(amountUsd: Money, exchangeRate: ExchangeRate) {
-        require(amountUsd.currency == "USD") { "Amount must be in USD" }
-        require(!amountUsd.isZero()) { "Amount must be greater than 0" }
-        require(amountUsd <= balanceUsd) { "Insufficient USD balance" }
+        require(!amountUsd.isZero()) { throw InvalidAmountException("Amount must be greater than 0") }
+        require(amountUsd <= balanceUsd) { throw InsufficientFundsException("Insufficient USD balance") }
+
         val amountPln = Money(exchangeRate.convertToPln(amountUsd.amount), "PLN")
         balanceUsd -= amountUsd
         balancePln += amountPln

src/main/kotlin/camilyed/github/io/currencyexchangeapi/domain/Exceptions.kt

@@ -0,0 +1,7 @@
+package camilyed.github.io.currencyexchangeapi.domain
+
+class InsufficientFundsException(message: String) : RuntimeException(message)
+
+class InvalidAmountException(message: String) : RuntimeException(message)
+
+class InvalidExchangeRateException(message: String) : RuntimeException(message)

src/main/kotlin/camilyed/github/io/currencyexchangeapi/domain/ExchangeRate.kt

@@ -6,7 +6,9 @@ import java.math.RoundingMode
 data class ExchangeRate(val rate: BigDecimal) {
 
     init {
-        require(rate > BigDecimal.ZERO) { "Exchange rate must be greater than 0" }
+        if (rate <= BigDecimal.ZERO) {
+            throw InvalidExchangeRateException("Exchange rate must be greater than 0")
+        }
     }
 
     fun convertFromPln(amountPln: BigDecimal): BigDecimal {

src/test/kotlin/camilyed/github/io/common/MoneyTest.kt

@@ -33,8 +33,8 @@ class MoneyTest {
         expectCatching {
             Money(BigDecimal("100.00"), "")
         }.isFailure()
-            .isA<IllegalArgumentException>()
-            .message.isEqualTo("Currency cannot be empty")
+            .isA<UnsupportedCurrencyException>()
+            .message.isEqualTo("Unsupported currency: ")
     }
 
     @Test

src/test/kotlin/camilyed/github/io/currencyexchangeapi/application/AccountServiceTest.kt

@@ -1,6 +1,9 @@
 package camilyed.github.io.currencyexchangeapi.application
 
 import camilyed.github.io.currencyexchangeapi.domain.AccountSnapshot
+import camilyed.github.io.currencyexchangeapi.domain.InsufficientFundsException
+import camilyed.github.io.currencyexchangeapi.domain.InvalidAmountException
+import camilyed.github.io.currencyexchangeapi.domain.InvalidExchangeRateException
 import camilyed.github.io.currencyexchangeapi.testing.ability.CreateAccountAbility
 import camilyed.github.io.currencyexchangeapi.testing.ability.SetNextAccountIdAbility
 import camilyed.github.io.currencyexchangeapi.testing.assertions.hasBalanceInPln
@@ -22,7 +25,6 @@ import strikt.assertions.isA
 import strikt.assertions.isEqualTo
 import strikt.assertions.isFailure
 import strikt.assertions.message
-import java.math.BigDecimal
 
 class AccountServiceTest : SetNextAccountIdAbility, CreateAccountAbility {
 
@@ -105,7 +107,7 @@ class AccountServiceTest : SetNextAccountIdAbility, CreateAccountAbility {
                     .withAmount("0.00")
             )
         }.isFailure()
-            .isA<IllegalArgumentException>()
+            .isA<InvalidAmountException>()
             .message.isEqualTo("Amount must be greater than 0")
     }
 
@@ -162,7 +164,7 @@ class AccountServiceTest : SetNextAccountIdAbility, CreateAccountAbility {
                     .withAmount("0.00")
             )
         }.isFailure()
-            .isA<IllegalArgumentException>()
+            .isA<InvalidAmountException>()
             .message.isEqualTo("Amount must be greater than 0")
     }
 
@@ -196,7 +198,7 @@ class AccountServiceTest : SetNextAccountIdAbility, CreateAccountAbility {
                     .withAmount("200.00")
             )
         }.isFailure()
-            .isA<IllegalArgumentException>()
+            .isA<InsufficientFundsException>()
             .message.isEqualTo("Insufficient PLN balance")
     }
 
@@ -213,7 +215,7 @@ class AccountServiceTest : SetNextAccountIdAbility, CreateAccountAbility {
                     .withAmount("100.00")
             )
         }.isFailure()
-            .isA<IllegalArgumentException>()
+            .isA<InsufficientFundsException>()
             .message.isEqualTo("Insufficient USD balance")
     }
 
@@ -268,7 +270,7 @@ class AccountServiceTest : SetNextAccountIdAbility, CreateAccountAbility {
                     .withExchangeRate("0.00")
             )
         }.isFailure()
-            .isA<IllegalArgumentException>()
+            .isA<InvalidExchangeRateException>()
             .message.isEqualTo("Exchange rate must be greater than 0")
     }