Add test case and refactor.

src/main/kotlin/com/mapk/kmapper/BoundKMapper.kt

@@ -38,16 +38,13 @@ class BoundKMapper<S : Any, D : Any> private constructor(
 
         parameters = function.requiredParameters
             .mapNotNull {
-                val temp = srcPropertiesMap[it.name]?.let { property ->
+                srcPropertiesMap[it.name]?.let { property ->
                     BoundParameterForMap.newInstance(it, property, parameterNameConverter)
+                }.apply {
+                    // 必須引数に対応するプロパティがsrcに定義されていない場合エラー
+                    if (this == null && !it.isOptional)
+                        throw IllegalArgumentException("Property ${it.name} is not declared in ${src.jvmName}.")
                 }
-
-                // 必須引数に対応するプロパティがsrcに定義されていない場合エラー
-                if (temp == null && !it.isOptional) {
-                    throw IllegalArgumentException("Property ${it.name} is not declared in ${src.jvmName}.")
-                }
-
-                temp
             }
     }
 

src/test/kotlin/com/mapk/kmapper/BoundKMapperInitTest.kt

@@ -0,0 +1,29 @@
+package com.mapk.kmapper
+
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertDoesNotThrow
+import org.junit.jupiter.api.assertThrows
+
+@Suppress("UNUSED_VARIABLE")
+@DisplayName("BoundKMapperの初期化時にエラーを吐かせるテスト")
+internal class BoundKMapperInitTest {
+    data class Dst1(val foo: Int, val bar: Short, val baz: Long)
+    data class Dst2(val foo: Int, val bar: Short, val baz: Long = 0)
+
+    data class Src(val foo: Int, val bar: Short)
+
+    @Test
+    @DisplayName("引数が足りない場合のエラーテスト")
+    fun isError() {
+        assertThrows<IllegalArgumentException> {
+            val mapper: BoundKMapper<Src, Dst1> = BoundKMapper()
+        }
+    }
+
+    @Test
+    @DisplayName("足りないのがオプショナルな引数の場合エラーにならないテスト")
+    fun isCollect() {
+        assertDoesNotThrow { val mapper: BoundKMapper<Src, Dst2> = BoundKMapper(::Dst2) }
+    }
+}

src/test/kotlin/com/mapk/kmapper/ConversionTest.kt

@@ -121,7 +121,7 @@ class ConversionTest {
         @DisplayName("Numberソース")
         fun fromNumber(numbers: NumberSource) {
             numbers.values.forEach {
-                val actual = BoundKMapper(::Dst, NumberSrc::class).map(NumberSrc(it))
+                val actual = BoundKMapper<NumberSrc, Dst>().map(NumberSrc(it))
                 assertEquals(0, BigDecimal.valueOf(it.toDouble()).compareTo(actual.number))
             }
         }
@@ -130,7 +130,7 @@ class ConversionTest {
         @ValueSource(strings = ["100", "2.0", "-500"])
         @DisplayName("Stringソース")
         fun fromString(str: String) {
-            val actual = BoundKMapper(::Dst, StringSrc::class).map(StringSrc(str))
+            val actual = BoundKMapper<StringSrc, Dst>().map(StringSrc(str))
             assertEquals(0, BigDecimal(str).compareTo(actual.number))
         }
     }