#449 Register error for duplicate key in Map property type

Author: ljacqu

src/main/java/ch/jalu/configme/properties/types/MapPropertyType.java

@@ -8,8 +8,8 @@
 import java.util.Map;
 
 /**
- * Property types for maps with strings as keys and any value type. The produced maps keep insertion order (as seen
- * in the property resource). Maps produced by this type never have a null key or null value.
+ * Property types for maps with strings as keys and any value type. The produced maps keep insertion order (as given
+ * in the property resource). Maps produced by this type never have a null key or a null value.
  *
  * @param <V> the type of values in the map
  */
@@ -40,7 +40,10 @@ public MapPropertyType(@NotNull PropertyType<V> valueType) {
             V value = valueType.convert(entry.getValue(), errorRecorder);
 
             if (key != null && value != null) {
-                map.put(key, value);
+                V previous = map.put(key, value);
+                if (previous != null) {
+                    errorRecorder.setHasError("Duplicate key detected: '" + key + "'");
+                }
             } else {
                 errorRecorder.setHasError("Key or value could not be converted for key '" + entry.getKey() + "'");
             }
@@ -57,7 +60,7 @@ public MapPropertyType(@NotNull PropertyType<V> valueType) {
         return exportMap;
     }
 
-    public @NotNull PropertyType<V> getValueType() {
+    public final @NotNull PropertyType<V> getValueType() {
         return valueType;
     }
 

src/test/java/ch/jalu/configme/properties/types/MapPropertyTypeTest.java

@@ -85,6 +85,28 @@ void shouldBuildMapAndSkipNullKey() {
         assertThat(errorRecorder.isFullyValid(), equalTo(false));
     }
 
+    @Test
+    void shouldRegisterErrorOnDuplicateKey() {
+        // given
+        MapPropertyType<TestEnum> mapType = new MapPropertyType<>(EnumPropertyType.of(TestEnum.class));
+        ConvertErrorRecorder errorRecorder = new ConvertErrorRecorder();
+
+        Map<Object, String> inputMap = new LinkedHashMap<>();
+        inputMap.put(1, "SECOND");
+        inputMap.put("3", "THIRD");
+        inputMap.put(3, "FIRST");
+
+        // when
+        Map<String, TestEnum> result = mapType.convert(inputMap, errorRecorder);
+
+        // then
+        assertThat(result, instanceOf(LinkedHashMap.class));
+        assertThat(result.keySet(), contains("1", "3"));
+        assertThat(result.get("1"), equalTo(TestEnum.SECOND));
+        assertThat(result.get("3"), equalTo(TestEnum.FIRST));
+        assertThat(errorRecorder.isFullyValid(), equalTo(false));
+    }
+
     @Test
     void shouldExportMap() {
         // given