adding config layer

extensions/diffs/src/config.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from "vitest";
+import { DEFAULT_DIFFS_TOOL_DEFAULTS, resolveDiffsPluginDefaults } from "./config.js";
+
+describe("resolveDiffsPluginDefaults", () => {
+  it("returns built-in defaults when config is missing", () => {
+    expect(resolveDiffsPluginDefaults(undefined)).toEqual(DEFAULT_DIFFS_TOOL_DEFAULTS);
+  });
+
+  it("applies configured defaults from plugin config", () => {
+    expect(
+      resolveDiffsPluginDefaults({
+        defaults: {
+          fontFamily: "JetBrains Mono",
+          fontSize: 17,
+          layout: "split",
+          wordWrap: false,
+          background: false,
+          theme: "light",
+          mode: "view",
+        },
+      }),
+    ).toEqual({
+      fontFamily: "JetBrains Mono",
+      fontSize: 17,
+      layout: "split",
+      wordWrap: false,
+      background: false,
+      theme: "light",
+      mode: "view",
+    });
+  });
+});