diff --git a/__tests__/installer.test.ts b/__tests__/installer.test.ts
index 5b4ae00..0551c46 100644
--- a/__tests__/installer.test.ts
+++ b/__tests__/installer.test.ts
@@ -1,18 +1,28 @@
-/* eslint @typescript-eslint/consistent-type-imports: 0 */
 import * as os from 'os';
 import * as path from 'path';
-import { IncomingMessage } from 'http';
+import { existsSync, promises as fs } from 'fs';
 
 import * as core from '@actions/core';
-import { HttpClient, HttpCodes } from '@actions/http-client';
+import * as hm from '@actions/http-client';
+import * as tc from '@actions/tool-cache';
 
 import * as installer from '../src/installer';
+import { getVersionFromToolcachePath } from '../src/utils';
 
 // Mocking modules
 jest.mock('@actions/core');
 
 const CACHE_PATH = path.join(__dirname, 'runner');
 
+function mockHttpClientGet(responseBody: string, statusCode = hm.HttpCodes.OK): void {
+  jest.spyOn(hm, 'HttpClient').mockReturnValue(({
+    get: jest.fn().mockResolvedValue({
+      message: { statusCode, statusMessage: '' },
+      readBody: jest.fn().mockResolvedValue(responseBody)
+    })
+  } as unknown) as hm.HttpClient);
+}
+
 function createXmlManifest(...versions: readonly string[]): string {
   return versions.map(ver => `<version>${ver}</version>`).join();
 }
@@ -32,10 +42,7 @@ describe('getAvailableVersions', () => {
   });
 
   it('failed to download versions manifest', async () => {
-    jest.spyOn(HttpClient.prototype, 'get').mockResolvedValue({
-      message: ({ statusCode: 0 } as unknown) as IncomingMessage,
-      readBody: jest.fn().mockResolvedValue('')
-    });
+    mockHttpClientGet('', 0);
 
     await expect(installer.getAvailableVersions()).rejects.toThrow(
       /Unable to get available versions from/i
@@ -48,10 +55,7 @@ describe('getAvailableVersions', () => {
       [` bar${createXmlManifest('')} foo`, []],
       [` ${createXmlManifest(' 1.x', 'foo')}!`, [' 1.x', 'foo']]
     ])('%s -> %j', async (xml: string, expected: readonly string[]) => {
-      jest.spyOn(HttpClient.prototype, 'get').mockResolvedValue({
-        message: ({ statusCode: HttpCodes.OK } as unknown) as IncomingMessage,
-        readBody: jest.fn().mockResolvedValue(xml)
-      });
+      mockHttpClientGet(xml);
 
       const availableVersions = await installer.getAvailableVersions();
       expect(availableVersions).toStrictEqual(expected);
@@ -69,10 +73,7 @@ describe('findVersionForDownload', () => {
       ['* ', ['foo', ' ', ' 1.0.x ', '3.0']],
       [' >=3', [' 2.0.1', '!', ' 3.0.x ', '3.3']]
     ])('%s %j', async (spec: string, versions: readonly string[]) => {
-      jest.spyOn(HttpClient.prototype, 'get').mockResolvedValue({
-        message: ({ statusCode: HttpCodes.OK } as unknown) as IncomingMessage,
-        readBody: jest.fn().mockResolvedValue(createXmlManifest(...versions))
-      });
+      mockHttpClientGet(createXmlManifest(...versions));
 
       await expect(installer.findVersionForDownload(spec)).rejects.toThrow(
         new RegExp(`not find.* version for.* ${spec}`, 'i')
@@ -86,10 +87,7 @@ describe('findVersionForDownload', () => {
       [' * ', ['!', '1.0.1', ' 3.1.0 ', '2.0.1 ', '3.3.0-alpha-1'], '3.1.0'],
       ['>=1 ', [' ', '1.1.0-beta-1', ' 1.0.1 ', ' 1.0.1-1'], '1.0.1']
     ])('%s %j -> %s', async (spec: string, versions: readonly string[], expected: string) => {
-      jest.spyOn(HttpClient.prototype, 'get').mockResolvedValue({
-        message: ({ statusCode: HttpCodes.OK } as unknown) as IncomingMessage,
-        readBody: jest.fn().mockResolvedValue(createXmlManifest(...versions))
-      });
+      mockHttpClientGet(createXmlManifest(...versions));
 
       const resolvedVersion = await installer.findVersionForDownload(spec);
       expect(resolvedVersion).toBe(expected);
@@ -98,13 +96,100 @@ describe('findVersionForDownload', () => {
   });
 });
 
-process.env.RUNNER_TEMP = os.tmpdir();
-process.env.RUNNER_TOOL_CACHE = CACHE_PATH;
+describe('download & setup Maven', () => {
+  process.env.RUNNER_TEMP = os.tmpdir();
+  process.env.RUNNER_TOOL_CACHE = CACHE_PATH;
 
-describe('downloadMaven', () => {
-  it.todo('download a real version of Maven');
+  afterEach(async () => {
+    await fs.rmdir(CACHE_PATH, { recursive: true });
+  });
 
-  it.todo('raises error if download failed');
+  describe('downloadMaven', () => {
+    const TEST_VERSION = '3.3.3';
 
-  it.todo('raises error when extracting failed');
+    it('download a real version of Maven', async () => {
+      const toolPath = await installer.downloadMaven(TEST_VERSION);
+
+      expect(core.info).toHaveBeenCalledWith(
+        expect.stringMatching(new RegExp(`Downloading Maven ${TEST_VERSION} from`, 'i'))
+      );
+
+      expect(existsSync(`${toolPath}.complete`)).toBe(true);
+      expect(existsSync(path.join(CACHE_PATH, 'maven', TEST_VERSION))).toBe(true);
+      expect(getVersionFromToolcachePath(toolPath)).toBe(TEST_VERSION);
+    });
+
+    it('raises error if download failed', async () => {
+      mockHttpClientGet('', 1);
+      await expect(installer.downloadMaven(TEST_VERSION)).rejects.toThrow(/Unexpected HTTP.* 1/i);
+
+      expect(core.info).toHaveBeenCalledTimes(1);
+      expect(core.debug).toHaveBeenCalledWith(
+        expect.stringMatching(/Failed to download.* Code\(1\)/i)
+      );
+    });
+
+    it('raises error when extracting failed', async () => {
+      const spyDownload = jest.spyOn(tc, 'downloadTool').mockResolvedValue(__filename);
+
+      await expect(installer.downloadMaven(TEST_VERSION)).rejects.toThrow(/failed.* exit code 1/i);
+
+      expect(spyDownload).toHaveBeenCalledWith(expect.stringContaining(TEST_VERSION));
+      expect(core.debug).toHaveBeenCalledWith(expect.stringContaining('tar'));
+    });
+  });
+
+  describe('setupMaven', () => {
+    const TEST_VERSION = '3.2.5';
+    const TOOL_PATH = path.join(CACHE_PATH, 'maven', TEST_VERSION, os.arch());
+
+    beforeEach(async () => {
+      await fs.mkdir(TOOL_PATH, { recursive: true });
+      await fs.writeFile(`${TOOL_PATH}.complete`, '');
+    });
+
+    describe('reuses the cached version of Maven', () => {
+      it.each([
+        [TEST_VERSION, TEST_VERSION.replace(/\d+$/, 'x '), undefined],
+        [TEST_VERSION, TEST_VERSION.replace(/\.\d+$/, ''), TEST_VERSION.replace(/\d+$/, '0 ')]
+      ])('%s <- %s', async (expected: string, spec: string, active?: string) => {
+        const resolvedVersion = await installer.setupMaven(spec, active);
+
+        expect(resolvedVersion).toBe(expected);
+        expect(core.addPath).toHaveBeenCalledWith(
+          expect.stringMatching(new RegExp(`\\b${expected}\\b.*[\\\\/]bin$`))
+        );
+      });
+    });
+
+    describe('uses version of system Maven', () => {
+      it.each([
+        [' 3.8', '3.8.2', ''],
+        ['3.x ', '3.3.9', TEST_VERSION]
+      ])('%s -> %s', async (spec: string, expected: string, resolved: string) => {
+        const resolvedVersion = await installer.setupMaven(spec, expected);
+
+        expect(resolvedVersion).toBe(expected);
+        expect(core.info).toHaveBeenCalledWith(
+          expect.stringMatching(new RegExp(`Use.* ${expected} instead of .*\\b${resolved}`, 'i'))
+        );
+        expect(core.addPath).not.toHaveBeenCalled();
+      });
+    });
+
+    it('install a new version of Maven', async () => {
+      const expected = '3.6.3';
+      mockHttpClientGet(createXmlManifest('3.5.2 ', ` ${expected}`, '3.6.1'));
+
+      jest.spyOn(tc, 'downloadTool').mockResolvedValue('');
+      jest.spyOn(tc, 'extractTar').mockResolvedValue('');
+      const spyCache = jest.spyOn(tc, 'cacheDir').mockResolvedValue('foo');
+
+      const resolvedVersion = await installer.setupMaven(' >3.5');
+
+      expect(spyCache).toHaveBeenCalledWith(expect.stringContaining(expected), 'maven', expected);
+      expect(resolvedVersion).toBe(expected);
+      expect(core.addPath).toHaveBeenCalledWith(path.join('foo', 'bin'));
+    });
+  });
 });
diff --git a/__tests__/main.test.ts b/__tests__/main.test.ts
index 43aea9c..7732ebf 100644
--- a/__tests__/main.test.ts
+++ b/__tests__/main.test.ts
@@ -1,15 +1,20 @@
+import * as os from 'os';
+import * as path from 'path';
+import { existsSync, promises as fs } from 'fs';
+
 import * as core from '@actions/core';
 
-import { getActiveMavenVersion } from '../src/utils';
-import { setupMaven } from '../src/installer';
+import * as utils from '../src/utils';
+import * as installer from '../src/installer';
 import { run } from '../src/main';
 
 // Mocking modules
 jest.mock('@actions/core');
-jest.mock('../src/utils');
-jest.mock('../src/installer');
 
+const MVN_PATH = path.join(__dirname, 'data');
 const DEFAULT_VERSION = '3';
+const REAL_VERSION = '3.5.2';
+const CACHE_PATH = path.join(__dirname, 'runner');
 
 describe('failed to run with invalid inputs', () => {
   it.each([
@@ -25,33 +30,83 @@ describe('failed to run with invalid inputs', () => {
 });
 
 describe('run with valid inputs', () => {
-  it('setups default version when no Maven is installed', async () => {
+  it.each([
+    // Default version + no Maven is installed
+    [{ setup: 'foo', spec: '' }, [DEFAULT_VERSION, undefined]],
+    [{ active: '', setup: '3.0', spec: ' * ' }, [' * ', '']],
+    // Installed version !~ version input
+    [{ active: '3.5.2', setup: DEFAULT_VERSION, spec: ' 3.3' }, [' 3.3', undefined]],
+    // Installed version =~ version input
+    [{ active: '3.3.9', setup: '', spec: '3.x ' }, ['3.x ', '3.3.9']]
+  ])(
+    '%o -> %j',
+    async (
+      version: Readonly<{ spec: string; active?: string; setup: string }>,
+      expected: readonly (string | undefined)[]
+    ) => {
+      (core.getInput as jest.Mock).mockReturnValue(version.spec);
+      jest.spyOn(utils, 'getActiveMavenVersion').mockResolvedValue(version.active);
+      const spySetup = jest.spyOn(installer, 'setupMaven').mockResolvedValue(version.setup);
+
+      await run();
+      expect(spySetup).toHaveBeenCalledWith(...expected);
+      expect(core.setOutput).toHaveBeenCalledWith('version', version.setup);
+    }
+  );
+});
+
+describe('integration tests', () => {
+  const ORIGINAL_PATH = process.env.PATH;
+  const TEST_VERSION = '3.1.1';
+  const TOOL_PATH = path.join(CACHE_PATH, 'maven', TEST_VERSION, os.arch());
+
+  process.env.RUNNER_TEMP = os.tmpdir();
+  process.env.RUNNER_TOOL_CACHE = CACHE_PATH;
+
+  beforeEach(() => {
+    process.env.PATH = `${MVN_PATH}${path.delimiter}${ORIGINAL_PATH ?? ''}`;
+  });
+
+  afterEach(async () => {
+    process.env.PATH = ORIGINAL_PATH;
+    await fs.rmdir(CACHE_PATH, { recursive: true });
+  });
+
+  it('uses system Maven if real version =~ default version', async () => {
     (core.getInput as jest.Mock).mockReturnValue('');
-    (getActiveMavenVersion as jest.Mock).mockResolvedValue(undefined);
-    (setupMaven as jest.Mock).mockResolvedValue('foo');
 
     await run();
-    expect(setupMaven).toHaveBeenCalledWith(DEFAULT_VERSION, undefined);
-    expect(core.setOutput).toHaveBeenCalledWith('version', 'foo');
+    expect(core.addPath).not.toHaveBeenCalled();
+    expect(core.setOutput).toHaveBeenCalledWith('version', REAL_VERSION);
   });
 
-  it('setups when installed Maven is different with version input', async () => {
-    (core.getInput as jest.Mock).mockReturnValue('3.3');
-    (getActiveMavenVersion as jest.Mock).mockResolvedValue('3.5.2');
-    (setupMaven as jest.Mock).mockResolvedValue(DEFAULT_VERSION);
+  it('install and cache a specific Maven version', async () => {
+    (core.getInput as jest.Mock).mockReturnValue(' ~3.1.0');
 
     await run();
-    expect(setupMaven).toHaveBeenCalledWith('3.3', undefined);
-    expect(core.setOutput).toHaveBeenCalledWith('version', DEFAULT_VERSION);
+    expect(core.info).toHaveBeenCalledWith(
+      expect.stringMatching(new RegExp(`Downloading Maven ${TEST_VERSION} from`, 'i'))
+    );
+
+    expect(core.addPath).toHaveBeenCalledWith(path.join(TOOL_PATH, 'bin'));
+    expect(core.setOutput).toHaveBeenCalledWith('version', TEST_VERSION);
+
+    expect(existsSync(`${TOOL_PATH}.complete`)).toBe(true);
   });
 
-  it('setups when installed Maven is correspond with version input', async () => {
-    (core.getInput as jest.Mock).mockReturnValue('3.x');
-    (getActiveMavenVersion as jest.Mock).mockResolvedValue('3.3.9');
-    (setupMaven as jest.Mock).mockResolvedValue('');
+  it('uses system Maven if real version > cached version', async () => {
+    await fs.mkdir(TOOL_PATH, { recursive: true });
+    await fs.writeFile(`${TOOL_PATH}.complete`, '');
+    (core.getInput as jest.Mock).mockReturnValue('3.x ');
 
     await run();
-    expect(setupMaven).toHaveBeenCalledWith('3.x', '3.3.9');
-    expect(core.setOutput).toHaveBeenCalledWith('version', '');
+    expect(core.info).toHaveBeenCalledWith(
+      expect.stringMatching(
+        new RegExp(`Use.* version ${REAL_VERSION} instead of.* ${TEST_VERSION}`, 'i')
+      )
+    );
+
+    expect(core.addPath).not.toHaveBeenCalled();
+    expect(core.setOutput).toHaveBeenCalledWith('version', REAL_VERSION);
   });
 });
diff --git a/__tests__/utils.test.ts b/__tests__/utils.test.ts
index 70806d2..878df42 100644
--- a/__tests__/utils.test.ts
+++ b/__tests__/utils.test.ts
@@ -11,6 +11,7 @@ jest.mock('child_process');
 jest.mock('@actions/core');
 
 const MVN_PATH = path.join(__dirname, 'data');
+const REAL_VERSION = '3.5.2';
 
 describe('getVersionFromToolcachePath', () => {
   it.each([
@@ -34,7 +35,6 @@ describe('getActiveMavenVersion', () => {
   });
 
   it('gets real version by `mvn` command', async () => {
-    const expectedVersion = '3.5.2';
     process.env.PATH = `${MVN_PATH}${path.delimiter}${ORIGINAL_PATH ?? ''}`;
 
     const cp = jest.requireActual<typeof child>('child_process');
@@ -42,9 +42,9 @@ describe('getActiveMavenVersion', () => {
 
     const installedVersion = await getActiveMavenVersion();
 
-    expect(installedVersion).toBe(expectedVersion);
+    expect(installedVersion).toBe(REAL_VERSION);
     expect(core.debug).toHaveBeenCalledWith(
-      expect.stringMatching(new RegExp(`Retrieved.* version: ${expectedVersion}`, 'i'))
+      expect.stringMatching(new RegExp(`Retrieved.* version: ${REAL_VERSION}`, 'i'))
     );
   });
 
@@ -75,7 +75,7 @@ describe('getActiveMavenVersion', () => {
   it('returns empty if `mvn` command is incorrect', async () => {
     process.env.PATH = MVN_PATH;
 
-    const cp = Object.create(new EventEmitter()) as EventEmitter & { stdout: EventEmitter };
+    const cp = (new EventEmitter() as unknown) as EventEmitter & { stdout: EventEmitter };
     (child.spawn as jest.Mock).mockReturnValue((cp.stdout = cp));
 
     setTimeout(() => cp.emit('data', 'foo') && cp.emit('close', 0), EMIT_AT);
diff --git a/jest.config.json b/jest.config.json
index 0d7e67a..39ab3d7 100644
--- a/jest.config.json
+++ b/jest.config.json
@@ -1,11 +1,12 @@
 {
   "clearMocks": true,
-  "resetMocks": true,
+  "restoreMocks": true,
   "moduleFileExtensions": ["ts", "js"],
   "testEnvironment": "node",
   "testMatch": ["**/*.test.ts"],
   "transform": {
     "\\.ts$": "ts-jest"
   },
+  "testTimeout": 15000,
   "verbose": true
 }