feat: migrate testing framework to Bun and update test configurations

- Updated GitHub Actions workflow to use Bun's test runner and coverage reporting.
- Added comprehensive testing documentation for the Gitea Mirror project.
- Refactored test scripts in package.json to align with Bun's testing commands.
- Created new test files for database, Gitea, GitHub, health, and mirroring APIs.
- Implemented mock functions for API tests to handle various scenarios and responses.
- Established a test setup file for consistent test environment configuration.

src/lib/utils.test.ts

@@ -0,0 +1,110 @@
+import { describe, test, expect } from "bun:test";
+import { jsonResponse, formatDate, truncate, safeParse } from "./utils";
+
+describe("jsonResponse", () => {
+  test("creates a Response with JSON content", () => {
+    const data = { message: "Hello, world!" };
+    const response = jsonResponse({ data });
+    
+    expect(response).toBeInstanceOf(Response);
+    expect(response.status).toBe(200);
+    expect(response.headers.get("Content-Type")).toBe("application/json");
+  });
+  
+  test("uses the provided status code", () => {
+    const data = { error: "Not found" };
+    const response = jsonResponse({ data, status: 404 });
+    
+    expect(response.status).toBe(404);
+  });
+  
+  test("correctly serializes complex objects", async () => {
+    const now = new Date();
+    const data = { 
+      message: "Complex object",
+      date: now,
+      nested: { foo: "bar" },
+      array: [1, 2, 3]
+    };
+    
+    const response = jsonResponse({ data });
+    const responseBody = await response.json();
+    
+    expect(responseBody).toEqual({
+      message: "Complex object",
+      date: now.toISOString(),
+      nested: { foo: "bar" },
+      array: [1, 2, 3]
+    });
+  });
+});
+
+describe("formatDate", () => {
+  test("formats a date object", () => {
+    const date = new Date("2023-01-15T12:30:45Z");
+    const formatted = formatDate(date);
+    
+    // The exact format might depend on the locale, so we'll check for parts
+    expect(formatted).toContain("2023");
+    expect(formatted).toContain("January");
+    expect(formatted).toContain("15");
+  });
+  
+  test("formats a date string", () => {
+    const dateStr = "2023-01-15T12:30:45Z";
+    const formatted = formatDate(dateStr);
+    
+    expect(formatted).toContain("2023");
+    expect(formatted).toContain("January");
+    expect(formatted).toContain("15");
+  });
+  
+  test("returns 'Never' for null or undefined", () => {
+    expect(formatDate(null)).toBe("Never");
+    expect(formatDate(undefined)).toBe("Never");
+  });
+});
+
+describe("truncate", () => {
+  test("truncates a string that exceeds the length", () => {
+    const str = "This is a long string that needs truncation";
+    const truncated = truncate(str, 10);
+    
+    expect(truncated).toBe("This is a ...");
+    expect(truncated.length).toBe(13); // 10 chars + "..."
+  });
+  
+  test("does not truncate a string that is shorter than the length", () => {
+    const str = "Short";
+    const truncated = truncate(str, 10);
+    
+    expect(truncated).toBe("Short");
+  });
+  
+  test("handles empty strings", () => {
+    expect(truncate("", 10)).toBe("");
+  });
+});
+
+describe("safeParse", () => {
+  test("parses valid JSON strings", () => {
+    const jsonStr = '{"name":"John","age":30}';
+    const parsed = safeParse(jsonStr);
+    
+    expect(parsed).toEqual({ name: "John", age: 30 });
+  });
+  
+  test("returns undefined for invalid JSON strings", () => {
+    const invalidJson = '{"name":"John",age:30}'; // Missing quotes around age
+    const parsed = safeParse(invalidJson);
+    
+    expect(parsed).toBeUndefined();
+  });
+  
+  test("returns the original value for non-string inputs", () => {
+    const obj = { name: "John", age: 30 };
+    const parsed = safeParse(obj);
+    
+    expect(parsed).toBe(obj);
+  });
+});