chore: add tests for schema and API config mocking

- Added unit tests for schema loader, mocking Config variables and resolvers.
- Added unit tests for Zabbix API configuration, verifying constants derived from Config.
- Mocked relevant modules and filesystem behaviors to enable isolated testing.
- Optimized imports on all files and include this within a new .junie/guidelines.md file

src/test/schema_config.test.ts

@@ -0,0 +1,41 @@
+import {schema_loader} from "../api/schema.js";
+import * as fs from "fs";
+import * as nodeFs from "node:fs";
+
+// Mocking Config
+jest.mock("../common_utils.js", () => ({
+    Config: {
+        SCHEMA_PATH: "./test_schema/",
+        ADDITIONAL_SCHEMAS: "./test_schema/extra.graphql",
+        ADDITIONAL_RESOLVERS: "ExtraDevice"
+    }
+}));
+
+// Mocking resolvers to avoid schema validation errors
+jest.mock("../api/resolvers.js", () => ({
+    createResolvers: jest.fn().mockReturnValue({
+        Query: {
+            test: () => "ok"
+        }
+    })
+}));
+
+// Mocking fs
+jest.mock("fs", () => ({
+    readFileSync: jest.fn().mockReturnValue("type Query { test: String } type Device { id: ID tags: [String] } type GenericDevice { id: ID tags: [String] } type DeviceConfig { id: ID } type ExtraDevice { id: ID tags: [String] }")
+}));
+
+jest.mock("node:fs", () => ({
+    readdirSync: jest.fn().mockReturnValue(["base.graphql"])
+}));
+
+describe("Schema Config Mocking", () => {
+    test("schema_loader uses Config variables", async () => {
+        const schema = await schema_loader();
+        
+        expect(nodeFs.readdirSync).toHaveBeenCalledWith("./test_schema/");
+        expect(fs.readFileSync).toHaveBeenCalledWith("./test_schema/base.graphql", expect.anything());
+        expect(fs.readFileSync).toHaveBeenCalledWith("./test_schema/extra.graphql", expect.anything());
+        expect(schema).toBeDefined();
+    });
+});