diff --git a/tests/plugins/esbuild.test.ts b/tests/plugins/esbuild.test.ts
new file mode 100644
index 0000000..58d720b
--- /dev/null
+++ b/tests/plugins/esbuild.test.ts
@@ -0,0 +1,150 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { yarnSpinnerPlugin } from '../../src/plugins/esbuild';
+import { resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = fileURLToPath(new URL('.', import.meta.url));
+
+describe('yarnSpinnerPlugin (esbuild)', () => {
+  // Fixtures are in tests/fixtures/, not tests/plugins/fixtures/
+  const projectPath = resolve(__dirname, '../fixtures/simple/.yarnproject');
+
+  it('should return an esbuild plugin with correct name', () => {
+    const plugin = yarnSpinnerPlugin();
+    expect(plugin.name).toBe('yarn-spinner-loader');
+  });
+
+  it('should have a setup function', () => {
+    const plugin = yarnSpinnerPlugin();
+    expect(plugin.setup).toBeDefined();
+    expect(typeof plugin.setup).toBe('function');
+  });
+
+  it('should register onLoad handler for .yarnproject files', () => {
+    const plugin = yarnSpinnerPlugin();
+
+    const mockBuild = {
+      onLoad: vi.fn((_options, callback) => {
+        // Store the callback for testing
+        (mockBuild as any)._onLoadCallback = callback;
+      }),
+    };
+
+    plugin.setup(mockBuild as any);
+
+    expect(mockBuild.onLoad).toHaveBeenCalledWith(
+      { filter: /\.yarnproject$/ },
+      expect.any(Function),
+    );
+  });
+
+  it('should load .yarnproject files and return correct content', async () => {
+    const plugin = yarnSpinnerPlugin();
+
+    let onLoadCallback: Function | undefined;
+    const mockBuild = {
+      onLoad: vi.fn((_options, callback) => {
+        onLoadCallback = callback;
+      }),
+    };
+
+    plugin.setup(mockBuild as any);
+
+    // Ensure callback was registered
+    expect(onLoadCallback).toBeDefined();
+
+    // Simulate esbuild calling the callback
+    const args = { path: projectPath };
+    const result = await (onLoadCallback as any)(args);
+
+    expect(result).toBeDefined();
+    expect(result.contents).toContain('export default');
+    expect(result.contents).toContain('project');
+    expect(result.contents).toContain('yarnFiles');
+    expect(result.loader).toBe('js');
+  });
+
+  it('should handle errors by returning error object', async () => {
+    const plugin = yarnSpinnerPlugin();
+
+    let onLoadCallback: Function | undefined;
+    const mockBuild = {
+      onLoad: vi.fn((_options, callback) => {
+        onLoadCallback = callback;
+      }),
+    };
+
+    plugin.setup(mockBuild as any);
+
+    // Simulate esbuild calling the callback with non-existent file
+    const args = { path: 'nonexistent/.yarnproject' };
+    const result = await (onLoadCallback as any)(args);
+
+    expect(result.errors).toBeDefined();
+    expect(result.errors.length).toBeGreaterThan(0);
+    expect(result.errors[0].text).toBeDefined();
+    expect(typeof result.errors[0].text).toBe('string');
+  });
+
+  it('should accept loadOptions and pass them to loadYarnProject', async () => {
+    const plugin = yarnSpinnerPlugin({
+      loadOptions: {
+        baseDir: resolve(__dirname, 'fixtures/simple'),
+      },
+    });
+
+    let onLoadCallback: Function | undefined;
+    const mockBuild = {
+      onLoad: vi.fn((_options, callback) => {
+        onLoadCallback = callback;
+      }),
+    };
+
+    plugin.setup(mockBuild as any);
+
+    const args = { path: projectPath };
+    const result = await (onLoadCallback as any)(args);
+
+    expect(result.contents).toContain('export default');
+    expect(result.loader).toBe('js');
+  });
+
+  it('should correctly serialize the result as JSON with proper formatting', async () => {
+    const plugin = yarnSpinnerPlugin();
+
+    let onLoadCallback: Function | undefined;
+    const mockBuild = {
+      onLoad: vi.fn((_options, callback) => {
+        onLoadCallback = callback;
+      }),
+    };
+
+    plugin.setup(mockBuild as any);
+
+    const args = { path: projectPath };
+    const result = await (onLoadCallback as any)(args);
+
+    // The contents should be properly formatted JavaScript code
+    expect(result.contents).toMatch(/export default {[\s\S]*};/);
+    expect(result.loader).toBe('js');
+  });
+
+  it('should handle non-Error objects in error handling', async () => {
+    const plugin = yarnSpinnerPlugin();
+
+    let onLoadCallback: Function | undefined;
+    const mockBuild = {
+      onLoad: vi.fn((_options, callback) => {
+        onLoadCallback = callback;
+      }),
+    };
+
+    plugin.setup(mockBuild as any);
+
+    const args = { path: 'nonexistent/.yarnproject' };
+    const result = await (onLoadCallback as any)(args);
+
+    expect(result.errors[0].text).toBeDefined();
+    expect(typeof result.errors[0].text).toBe('string');
+  });
+});
diff --git a/tests/plugins/rollup.test.ts b/tests/plugins/rollup.test.ts
new file mode 100644
index 0000000..5597f71
--- /dev/null
+++ b/tests/plugins/rollup.test.ts
@@ -0,0 +1,104 @@
+import { describe, it, expect, vi } from 'vitest';
+import { yarnSpinnerRollup } from '../../src/plugins/rollup';
+import { resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = fileURLToPath(new URL('.', import.meta.url));
+
+describe('yarnSpinnerRollup', () => {
+  // Fixtures are in tests/fixtures/, not tests/plugins/fixtures/
+  const projectPath = resolve(__dirname, '../fixtures/simple/.yarnproject');
+
+  it('should return a Rollup plugin with correct name', () => {
+    const plugin = yarnSpinnerRollup();
+    expect(plugin.name).toBe('yarn-spinner-loader');
+  });
+
+  it('should have a load function', () => {
+    const plugin = yarnSpinnerRollup();
+    expect(plugin.load).toBeDefined();
+    expect(typeof plugin.load).toBe('function');
+  });
+
+  it('should load .yarnproject files and return exported code', async () => {
+    const plugin = yarnSpinnerRollup();
+    const loadFn = plugin.load as Function;
+
+    const mockContext = {
+      error: vi.fn(),
+    };
+
+    const result = await loadFn.call(mockContext, projectPath);
+
+    // If error was called, the file wasn't found or was invalid
+    if (mockContext.error.mock.calls.length > 0) {
+      throw new Error(mockContext.error.mock.calls[0][0]);
+    }
+
+    expect(result).toBeDefined();
+    expect(typeof result).toBe('string');
+    expect(result).toContain('export default');
+    expect(result).toContain('project');
+    expect(result).toContain('yarnFiles');
+  });
+
+  it('should return null for non-.yarnproject files', async () => {
+    const plugin = yarnSpinnerRollup();
+    const loadFn = plugin.load as Function;
+
+    const result = await loadFn.call({}, 'some-file.ts');
+
+    expect(result).toBeNull();
+  });
+
+  it('should handle errors by calling this.error', async () => {
+    const plugin = yarnSpinnerRollup();
+    const loadFn = plugin.load as Function;
+
+    const mockThis = {
+      error: vi.fn(),
+    };
+
+    await loadFn.call(mockThis, 'nonexistent/.yarnproject');
+
+    expect(mockThis.error).toHaveBeenCalled();
+  });
+
+  it('should accept loadOptions and pass them to loadYarnProject', async () => {
+    const plugin = yarnSpinnerRollup({
+      loadOptions: {
+        baseDir: resolve(__dirname, '../fixtures/simple'),
+      },
+    });
+    const loadFn = plugin.load as Function;
+
+    const mockContext = {
+      error: vi.fn(),
+    };
+
+    const result = await loadFn.call(mockContext, projectPath);
+
+    expect(mockContext.error).not.toHaveBeenCalled();
+    expect(result).toBeDefined();
+    expect(typeof result).toBe('string');
+    expect(result).toContain('export default');
+  });
+
+  it('should correctly serialize the result as JSON', async () => {
+    const plugin = yarnSpinnerRollup();
+    const loadFn = plugin.load as Function;
+
+    const mockContext = {
+      error: vi.fn(),
+    };
+
+    const result = await loadFn.call(mockContext, projectPath);
+
+    if (mockContext.error.mock.calls.length > 0) {
+      throw new Error(mockContext.error.mock.calls[0][0]);
+    }
+
+    // The result should be valid JavaScript code
+    expect(result).toMatch(/export default {[\s\S]*};/);
+  });
+});
diff --git a/tests/plugins/vite.test.ts b/tests/plugins/vite.test.ts
new file mode 100644
index 0000000..ecc653c
--- /dev/null
+++ b/tests/plugins/vite.test.ts
@@ -0,0 +1,113 @@
+import { describe, it, expect, vi } from 'vitest';
+import { yarnSpinnerVite } from '../../src/plugins/vite';
+import { resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = fileURLToPath(new URL('.', import.meta.url));
+
+describe('yarnSpinnerVite', () => {
+  // Fixtures are in tests/fixtures/, not tests/plugins/fixtures/
+  const projectPath = resolve(__dirname, '../fixtures/simple/.yarnproject');
+
+  it('should return a Vite plugin with correct name', () => {
+    const plugin = yarnSpinnerVite();
+    expect(plugin.name).toBe('yarn-spinner-loader');
+  });
+
+  it('should have a load function', () => {
+    const plugin = yarnSpinnerVite();
+    expect(plugin.load).toBeDefined();
+    expect(typeof plugin.load).toBe('function');
+  });
+
+  it('should load .yarnproject files and return exported code', async () => {
+    const plugin = yarnSpinnerVite();
+    const loadFn = plugin.load as Function;
+
+    const mockContext = {
+      error: vi.fn(),
+    };
+
+    const result = await loadFn.call(mockContext, projectPath);
+
+    // If error was called, the file wasn't found or was invalid
+    if (mockContext.error.mock.calls.length > 0) {
+      throw new Error(mockContext.error.mock.calls[0][0]);
+    }
+
+    expect(result).toBeDefined();
+    expect(typeof result).toBe('string');
+    expect(result).toContain('export default');
+    expect(result).toContain('project');
+    expect(result).toContain('yarnFiles');
+  });
+
+  it('should return null for non-.yarnproject files', async () => {
+    const plugin = yarnSpinnerVite();
+    const loadFn = plugin.load as Function;
+
+    const result = await loadFn.call({}, 'some-file.ts');
+
+    expect(result).toBeNull();
+  });
+
+  it('should handle errors by calling this.error', async () => {
+    const plugin = yarnSpinnerVite();
+    const loadFn = plugin.load as Function;
+
+    const mockThis = {
+      error: vi.fn(),
+    };
+
+    await loadFn.call(mockThis, 'nonexistent/.yarnproject');
+
+    expect(mockThis.error).toHaveBeenCalled();
+  });
+
+  it('should accept loadOptions and pass them to loadYarnProject', async () => {
+    const plugin = yarnSpinnerVite({
+      loadOptions: {
+        baseDir: resolve(__dirname, '../fixtures/simple'),
+      },
+    });
+    const loadFn = plugin.load as Function;
+
+    const mockContext = {
+      error: vi.fn(),
+    };
+
+    const result = await loadFn.call(mockContext, projectPath);
+
+    expect(mockContext.error).not.toHaveBeenCalled();
+    expect(result).toBeDefined();
+    expect(typeof result).toBe('string');
+    expect(result).toContain('export default');
+  });
+
+  it('should have a transform function', () => {
+    const plugin = yarnSpinnerVite();
+    expect(plugin.transform).toBeDefined();
+    expect(typeof plugin.transform).toBe('function');
+  });
+
+  it('transform should return empty export for .yarnproject files', () => {
+    const plugin = yarnSpinnerVite();
+    const transformFn = plugin.transform as Function;
+
+    const result = transformFn.call({}, 'console.log("test")', projectPath);
+
+    expect(result).toEqual({
+      code: 'export default {};',
+      map: null,
+    });
+  });
+
+  it('transform should return null for non-.yarnproject files', () => {
+    const plugin = yarnSpinnerVite();
+    const transformFn = plugin.transform as Function;
+
+    const result = transformFn.call({}, 'console.log("test")', 'some-file.ts');
+
+    expect(result).toBeNull();
+  });
+});
diff --git a/tests/plugins/webpack.test.ts b/tests/plugins/webpack.test.ts
new file mode 100644
index 0000000..ad529e8
--- /dev/null
+++ b/tests/plugins/webpack.test.ts
@@ -0,0 +1,98 @@
+import { describe, it, expect, vi } from 'vitest';
+import { YarnSpinnerWebpackLoader } from '../../src/plugins/webpack';
+import { resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = fileURLToPath(new URL('.', import.meta.url));
+
+describe('YarnSpinnerWebpackLoader', () => {
+  // Fixtures are in tests/fixtures/, not tests/plugins/fixtures/
+  const projectPath = resolve(__dirname, '../fixtures/simple/.yarnproject');
+
+  it('should be a function', () => {
+    expect(typeof YarnSpinnerWebpackLoader).toBe('function');
+  });
+
+  it('should load .yarnproject files and return exported JSON', function () {
+    const mockContext = {
+      getOptions: vi.fn().mockReturnValue({}),
+      resourcePath: projectPath,
+      emitError: vi.fn(),
+    };
+
+    const result = YarnSpinnerWebpackLoader.call(mockContext, '');
+
+    expect(result).toBeDefined();
+    expect(typeof result).toBe('string');
+    expect(result).toContain('export default');
+    expect(result).toContain('project');
+    expect(result).toContain('yarnFiles');
+    // Ensure no errors were emitted
+    expect(mockContext.emitError).not.toHaveBeenCalled();
+  });
+
+  it('should pass loadOptions to loadYarnProjectSync', function () {
+    const mockContext = {
+      getOptions: vi.fn().mockReturnValue({
+        loadOptions: {
+          baseDir: resolve(__dirname, 'fixtures/simple'),
+        },
+      }),
+      resourcePath: projectPath,
+      emitError: vi.fn(),
+    };
+
+    const result = YarnSpinnerWebpackLoader.call(mockContext, '');
+
+    expect(result).toContain('export default');
+    expect(mockContext.emitError).not.toHaveBeenCalled();
+  });
+
+  it('should handle errors by calling emitError', function () {
+    const mockContext = {
+      getOptions: vi.fn().mockReturnValue({}),
+      resourcePath: 'nonexistent/.yarnproject',
+      emitError: vi.fn(),
+    };
+
+    const originalSource = '// original source';
+    const result = YarnSpinnerWebpackLoader.call(mockContext, originalSource);
+
+    expect(mockContext.emitError).toHaveBeenCalled();
+    expect(mockContext.emitError).toHaveBeenCalledWith(expect.any(Error));
+    // Should return original source on error
+    expect(result).toBe(originalSource);
+  });
+
+  it('should return original source on error', function () {
+    const originalSource = '// original source';
+    const mockContext = {
+      getOptions: vi.fn().mockReturnValue({}),
+      resourcePath: 'nonexistent/.yarnproject',
+      emitError: vi.fn(),
+    };
+
+    const result = YarnSpinnerWebpackLoader.call(mockContext, originalSource);
+
+    expect(result).toBe(originalSource);
+  });
+
+  it('should handle non-Error objects in error handling', function () {
+    const mockContext = {
+      getOptions: vi.fn().mockReturnValue({}),
+      resourcePath: 'nonexistent/.yarnproject',
+      emitError: vi.fn(),
+    };
+
+    YarnSpinnerWebpackLoader.call(mockContext, '');
+
+    expect(mockContext.emitError).toHaveBeenCalled();
+    const emittedError = mockContext.emitError.mock.calls[0][0];
+    expect(emittedError).toBeInstanceOf(Error);
+  });
+
+  it('should have a default export', () => {
+    // Import using ESM to check default export
+    expect(YarnSpinnerWebpackLoader).toBeDefined();
+  });
+});