diff --git a/server/src/score-import/import-types/file/mer-iidx/converter.test.ts b/server/src/score-import/import-types/file/mer-iidx/converter.test.ts
new file mode 100644
index 000000000..0d68d7353
--- /dev/null
+++ b/server/src/score-import/import-types/file/mer-iidx/converter.test.ts
@@ -0,0 +1,16 @@
+import t from "tap";
+import { CloseMongoConnection } from "../../../../db/db";
+import ResetDBState from "../../../../test-utils/reset-db-state";
+import { ConvertFileMerIIDX } from "./converter";
+
+t.test("#ConvertFileMerIIDX", (t) => {
+    t.beforeEach(ResetDBState);
+
+    t.test("", (t) => {
+        t.end();
+    });
+
+    t.end();
+});
+
+t.teardown(CloseMongoConnection);
diff --git a/server/src/score-import/import-types/file/mer-iidx/parser.test.ts b/server/src/score-import/import-types/file/mer-iidx/parser.test.ts
new file mode 100644
index 000000000..08967a5c6
--- /dev/null
+++ b/server/src/score-import/import-types/file/mer-iidx/parser.test.ts
@@ -0,0 +1,94 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import t from "tap";
+import { CloseMongoConnection } from "../../../../db/db";
+import CreateLogCtx from "../../../../logger";
+import { MockMulterFile } from "../../../../test-utils/mock-multer";
+import ResetDBState from "../../../../test-utils/reset-db-state";
+import { GetKTDataBuffer } from "../../../../test-utils/test-data";
+import { ParseMerIIDX } from "./parser";
+
+const logger = CreateLogCtx("parser.test.ts");
+
+t.test("#ParseMerIIDX", (t) => {
+    t.beforeEach(ResetDBState);
+
+    function mrfb(buffer: Buffer) {
+        return ParseMerIIDX(MockMulterFile(buffer, "buffer.json"), {}, logger);
+    }
+
+    function mrff(filename: string) {
+        return ParseMerIIDX(MockMulterFile(GetKTDataBuffer(filename), filename), {}, logger);
+    }
+
+    // @todo Better tests for invalidating bad input?
+
+    t.test("Basic Parsing", (t) => {
+        const res = mrff("./mer/base.json");
+
+        t.hasStrict(
+            res,
+            {
+                game: "iidx",
+                context: {},
+                classHandler: null,
+                iterable: [
+                    {
+                        music_id: 3007,
+                        music_name: "Presto",
+                        play_type: "SINGLE",
+                        diff_type: "HYPER",
+                        score: 566,
+                        miss_count: 46,
+                        clear_type: "NO PLAY",
+                        update_time: "2019-06-01 19:56:59",
+                    },
+                    {
+                        music_id: 3013,
+                        music_name: "THE SAFARI",
+                        play_type: "SINGLE",
+                        diff_type: "NORMAL",
+                        score: 681,
+                        miss_count: 102,
+                        clear_type: "FAILED",
+                        update_time: "2019-05-30 03:21:57",
+                    },
+                    {
+                        music_id: 3213,
+                        music_name: "TAKE ON ME",
+                        play_type: "SINGLE",
+                        diff_type: "ANOTHER",
+                        score: 922,
+                        miss_count: 56,
+                        clear_type: "CLEAR",
+                        update_time: "2019-05-03 02:10:58",
+                    },
+                ],
+            } as any,
+            "Should correctly parse data."
+        );
+
+        t.end();
+    });
+
+    t.test("Should throw on invalid JSON", (t) => {
+        t.throws(() => mrfb(Buffer.from("{]")));
+
+        t.end();
+    });
+
+    t.test("Should throw on non-top-level-array", (t) => {
+        t.throws(() => mrfb(Buffer.from("{}")));
+
+        t.end();
+    });
+
+    t.test("Should throw on invalid Mer Scores", (t) => {
+        t.throws(() => mrfb(Buffer.from(JSON.stringify([{ foo: "bar" }]))));
+
+        t.end();
+    });
+
+    t.end();
+});
+
+t.teardown(CloseMongoConnection);
diff --git a/server/src/score-import/import-types/file/mer-iidx/parser.ts b/server/src/score-import/import-types/file/mer-iidx/parser.ts
index b0c6a769b..3d3646cfa 100644
--- a/server/src/score-import/import-types/file/mer-iidx/parser.ts
+++ b/server/src/score-import/import-types/file/mer-iidx/parser.ts
@@ -34,7 +34,7 @@ export function ParseMerIIDX(
     try {
         jsonData = JSON.parse(fileData.buffer.toString("utf-8"));
     } catch (err) {
-        logger.info(err);
+        logger.info(err.message);
         throw new ScoreImportFatalError(400, "Invalid JSON.");
     }
 
@@ -47,7 +47,7 @@ export function ParseMerIIDX(
         const err = p(jsonData[i], PR_MerIIDX, {}, { allowExcessKeys: true });
 
         if (err) {
-            throw new ScoreImportFatalError(400, FormatPrError(err));
+            throw new ScoreImportFatalError(400, `${FormatPrError(err)} [Index ${i}]`);
         }
     }