Provide test cases for issue #2158 (#3111)

src/test/java/com/fasterxml/jackson/failing/JsonCreatorMapKeyDeserialization2158Test.java

@@ -0,0 +1,71 @@
+package com.fasterxml.jackson.failing;
+
+import static org.junit.Assert.assertThrows;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonValue;
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.BaseMapTest;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.exc.InvalidFormatException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Objects;
+
+// For [databind#2158]: The default map key deserializer bypasses `@JsonCreator` methods in favour
+// of direct constructor invocation.
+public class JsonCreatorMapKeyDeserialization2158Test extends BaseMapTest {
+    private static final TypeReference<Map<DummyDto, Integer>> MAP_TYPE_REFERENCE =
+            new TypeReference<Map<DummyDto, Integer>>() {};
+
+    public void testDeserializeInvalidKey() {
+        ObjectMapper mapper = new ObjectMapper();
+        InvalidFormatException exception =
+                assertThrows(
+                        InvalidFormatException.class,
+                        () -> mapper.readValue("{ \"\": 0 }", MAP_TYPE_REFERENCE));
+        assertTrue(exception.getMessage().contains("Value must be nonempty"));
+    }
+
+    public void testNormalizeKey() {
+        ObjectMapper mapper = new ObjectMapper();
+        assertEquals(
+                Collections.singletonMap(DummyDto.fromValue("foo"), 0),
+                mapper.readValue("{ \"FOO\": 0 }", MAP_TYPE_REFERENCE));
+    }
+
+    private static final class DummyDto {
+        @JsonValue
+        private final String value;
+
+        private DummyDto(String value) {
+            this.value = value;
+        }
+
+        @JsonCreator
+        static DummyDto fromValue(String value) {
+            if (value.isEmpty()) {
+                throw new IllegalArgumentException("Value must be nonempty");
+            }
+
+            return new DummyDto(value.toLowerCase(Locale.ROOT));
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            return o instanceof DummyDto && ((DummyDto) o).value.equals(value);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(value);
+        }
+
+        @Override
+        public String toString() {
+            return String.format("DummyDto{value=%s}", value);
+        }
+    }
+}