diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f08e8b2e..e581b50c 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -8,11 +8,10 @@ on:
 jobs:
   test:
     runs-on: macOS-latest
+    timeout-minutes: 20
     strategy:
       matrix:
-        api-level: [28, 29]
-        target: [default, google_apis]
-        abi: [x86, x86_64]
+        api-level: [21, 29]
     steps:
     - name: checkout
       uses: actions/checkout@v1
@@ -29,6 +28,6 @@ jobs:
       uses: ./
       with: 
         api-level: ${{ matrix.api-level }}
-        target: ${{ matrix.target }}
-        abi: ${{ matrix.abi }}
+        target: default
+        abi: x86
         headless: true
diff --git a/__tests__/input-validator.test.ts b/__tests__/input-validator.test.ts
new file mode 100644
index 00000000..b3f519cc
--- /dev/null
+++ b/__tests__/input-validator.test.ts
@@ -0,0 +1,71 @@
+import * as validator from '../src/input-validator';
+
+describe('api-level validator tests', () => {
+  it('Throws if api-level is not a number', () => {
+    const func = function() { validator.checkApiLevel('api'); }
+    expect(func).toThrowError(`Unexpected API level: 'api'.`);
+  });
+
+  it('Throws if api-level is not an integer', () => {
+    const func = function() { validator.checkApiLevel('29.1'); }
+    expect(func).toThrowError(`Unexpected API level: '29.1'.`);
+  });
+
+  it('Throws if api-level is lower than min API supported', () => {
+    const func = function() { validator.checkApiLevel('20'); }
+    expect(func).toThrowError(`Minimum API level supported is ${validator.MIN_API_LEVEL}.`);
+  });
+
+  it('Validates successfully with valid api-level', () => {
+    const func1 = function() { validator.checkApiLevel('21'); }
+    expect(func1).not.toThrow();
+
+    const func2 = function() { validator.checkApiLevel('29'); }
+    expect(func2).not.toThrow();
+  });
+});
+
+describe('target validator tests', () => {
+  it('Throws if target is unknown', () => {
+    const func = function() { validator.checkTarget('some-target'); }
+    expect(func).toThrowError(`Value for input.target 'some-target' is unknown. Supported options: ${validator.VALID_TARGETS}`);
+  });
+
+  it('Validates successfully with valid target', () => {
+    const func1 = function() { validator.checkTarget('default'); }
+    expect(func1).not.toThrow();
+
+    const func2 = function() { validator.checkTarget('google_apis'); }
+    expect(func2).not.toThrow();
+  });
+});
+
+describe('abi validator tests', () => {
+  it('Throws if abi is unknown', () => {
+    const func = function() { validator.checkAbi('some-abi'); }
+    expect(func).toThrowError(`Value for input.abi 'some-abi' is unknown. Supported options: ${validator.VALID_ABIS}`);
+  });
+
+  it('Validates successfully with valid abi', () => {
+    const func1 = function() { validator.checkAbi('x86'); }
+    expect(func1).not.toThrow();
+
+    const func2 = function() { validator.checkAbi('x86_64'); }
+    expect(func2).not.toThrow();
+  });
+});
+
+describe('headless validator tests', () => {
+  it('Throws if headless is not a boolean', () => {
+    const func = function() { validator.checkHeadless('yes'); }
+    expect(func).toThrowError(`Input for input.headless should be either 'true' or 'false'.`);
+  });
+
+  it('Validates successfully if headless is either true or false', () => {
+    const func1 = function() { validator.checkHeadless('true'); }
+    expect(func1).not.toThrow();
+
+    const func2 = function() { validator.checkHeadless('false'); }
+    expect(func2).not.toThrow();
+  });
+});
diff --git a/__tests__/main.test.ts b/__tests__/main.test.ts
deleted file mode 100644
index 7d18ab3a..00000000
--- a/__tests__/main.test.ts
+++ /dev/null
@@ -1,3 +0,0 @@
-test('test action inputs', async() => {
-    // TODO
-});
diff --git a/action.yml b/action.yml
index 87c5ea7f..60d403bb 100644
--- a/action.yml
+++ b/action.yml
@@ -7,7 +7,7 @@ inputs:
     required: true
   target:
     description: 'target of the system image - default of google_apis'
-    default: 'google_apis'
+    default: 'default'
   abi:
     description: 'cpu/abi of the system image - x86 or x86_64'
     default: 'x86'
diff --git a/lib/input-validator.js b/lib/input-validator.js
new file mode 100644
index 00000000..98bfd751
--- /dev/null
+++ b/lib/input-validator.js
@@ -0,0 +1,32 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.MIN_API_LEVEL = 21;
+exports.VALID_TARGETS = ['default', 'google_apis'];
+exports.VALID_ABIS = ['x86', 'x86_64'];
+function checkApiLevel(apiLevel) {
+    if (isNaN(Number(apiLevel)) || !Number.isInteger(Number(apiLevel))) {
+        throw new Error(`Unexpected API level: '${apiLevel}'.`);
+    }
+    if (Number(apiLevel) < exports.MIN_API_LEVEL) {
+        throw new Error(`Minimum API level supported is ${exports.MIN_API_LEVEL}.`);
+    }
+}
+exports.checkApiLevel = checkApiLevel;
+function checkTarget(target) {
+    if (!exports.VALID_TARGETS.includes(target)) {
+        throw new Error(`Value for input.target '${target}' is unknown. Supported options: ${exports.VALID_TARGETS}.`);
+    }
+}
+exports.checkTarget = checkTarget;
+function checkAbi(abi) {
+    if (!exports.VALID_ABIS.includes(abi)) {
+        throw new Error(`Value for input.abi '${abi}' is unknown. Supported options: ${exports.VALID_ABIS}.`);
+    }
+}
+exports.checkAbi = checkAbi;
+function checkHeadless(headless) {
+    if (headless !== 'true' && headless !== 'false') {
+        throw new Error(`Input for input.headless should be either 'true' or 'false'.`);
+    }
+}
+exports.checkHeadless = checkHeadless;
diff --git a/lib/main.js b/lib/main.js
index cdb6ec7a..b9cd281a 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -17,6 +17,7 @@ var __importStar = (this && this.__importStar) || function (mod) {
 Object.defineProperty(exports, "__esModule", { value: true });
 const core = __importStar(require("@actions/core"));
 const sdk_installer_1 = require("./sdk-installer");
+const input_validator_1 = require("./input-validator");
 function run() {
     return __awaiter(this, void 0, void 0, function* () {
         try {
@@ -24,31 +25,22 @@ function run() {
             if (process.platform !== 'darwin') {
                 throw new Error('This action is expected to be run within a macOS virtual machine to enable hardware acceleration.');
             }
-            // TODO test inputs
-            // TODO test real inputs in test.yml
-            // api-level is required
-            // TODO use InputOptions {true}
-            const apiLevel = core.getInput('api-level');
-            // TODO check apiLevel is number and within valid range
-            console.log(`API level - ${apiLevel}`);
-            // target is optional with default
+            // API level of the platform and system image
+            const apiLevel = core.getInput('api-level', { required: true });
+            input_validator_1.checkApiLevel(apiLevel);
+            console.log(`API level: ${apiLevel}`);
+            // target of the system image
             const target = core.getInput('target');
-            if (target !== 'default' && target !== 'google_apis') {
-                throw new Error(`Target ${target} is unknown. Please use either 'default' or 'google_apis'.`);
-            }
-            console.log(`target - ${target}`);
-            // abi is optional with default
+            input_validator_1.checkTarget(target);
+            console.log(`target: ${target}`);
+            // CPU / ABI of the system image
             const abi = core.getInput('abi');
-            if (abi !== 'x86' && abi !== 'x86_64') {
-                throw new Error(`abi ${abi} is unknown (ARM-based emulators are not supported). Please use either 'x86' or 'x86_64'.`);
-            }
-            console.log(`cpu/abi - ${abi}`);
-            // headless is optional with default
+            input_validator_1.checkAbi(abi);
+            console.log(`cpu/abi: ${abi}`);
+            // headless mode
             const headless = core.getInput('headless');
-            if (headless !== 'true' && headless !== 'false') {
-                throw new Error(`Input 'headless' should be either 'true' or 'false'.`);
-            }
-            console.log(`headless mode - ${headless}`);
+            input_validator_1.checkHeadless(headless);
+            console.log(`headless mode: ${headless}`);
             // install SDK
             yield sdk_installer_1.installAndroidSdk(Number(apiLevel), target, abi);
             // TODO start emulator
diff --git a/lib/sdk-installer.js b/lib/sdk-installer.js
index 965f34c9..338dfe39 100644
--- a/lib/sdk-installer.js
+++ b/lib/sdk-installer.js
@@ -24,7 +24,7 @@ const SDK_URL = 'https://dl.google.com/android/repository/sdk-tools-darwin-43337
  * Downloads and installs the Android SDK for the macOS platform, including SDK platform for the chosen API level, latest build tools, platform tools, Android Emulator,
  * and the system image for the chosen API level, cpu/abi, and target.
  */
-function installAndroidSdk(apiLevel, abi, target) {
+function installAndroidSdk(apiLevel, target, abi) {
     return __awaiter(this, void 0, void 0, function* () {
         // download Android SDK if not already installed
         if (fs.existsSync(`${process.env.ANDROID_HOME}/tools/bin/sdkmanager`)) {
@@ -37,8 +37,7 @@ function installAndroidSdk(apiLevel, abi, target) {
         }
         // install specific SDK tools
         console.log('Installing build tools, platform tools, platform and system image.');
-        yield exec.exec(`yes | ${process.env.ANDROID_HOME}/tools/bin/sdkmanager --licenses`);
-        yield exec.exec(`${process.env.ANDROID_HOME}/tools/bin/sdkmanager --update`);
+        yield exec.exec(`echo "y" | ${process.env.ANDROID_HOME}/tools/bin/sdkmanager --licenses > /dev/null`);
         yield exec.exec(`${process.env.ANDROID_HOME}/tools/bin/sdkmanager "build-tools;${BUILD_TOOLS_VERSION}"`);
         yield exec.exec(`${process.env.ANDROID_HOME}/tools/bin/sdkmanager "platform-tools"`);
         yield exec.exec(`${process.env.ANDROID_HOME}/tools/bin/sdkmanager "platforms;android-${apiLevel}"`);
diff --git a/src/input-validator.ts b/src/input-validator.ts
new file mode 100644
index 00000000..8d004990
--- /dev/null
+++ b/src/input-validator.ts
@@ -0,0 +1,32 @@
+import { isNumber } from "util";
+
+export const MIN_API_LEVEL = 21;
+export const VALID_TARGETS: Array<string> = ['default', 'google_apis'];
+export const VALID_ABIS: Array<string> = ['x86', 'x86_64'];
+
+export function checkApiLevel(apiLevel: string): void {
+  if (isNaN(Number(apiLevel)) || !Number.isInteger(Number(apiLevel))) {
+    throw new Error(`Unexpected API level: '${apiLevel}'.`);
+  }
+  if (Number(apiLevel) < MIN_API_LEVEL) {
+    throw new Error(`Minimum API level supported is ${MIN_API_LEVEL}.`);
+  }
+}
+
+export function checkTarget(target: string): void {
+  if (!VALID_TARGETS.includes(target)) {
+    throw new Error(`Value for input.target '${target}' is unknown. Supported options: ${VALID_TARGETS}.`);
+  }
+}
+
+export function checkAbi(abi: string): void {
+  if (!VALID_ABIS.includes(abi)) {
+    throw new Error(`Value for input.abi '${abi}' is unknown. Supported options: ${VALID_ABIS}.`);
+  }
+}
+
+export function checkHeadless(headless: string): void {
+  if (headless !== 'true' && headless !== 'false') {
+    throw new Error(`Input for input.headless should be either 'true' or 'false'.`);
+  }
+}
diff --git a/src/main.ts b/src/main.ts
index 707b7fb9..f23fb9de 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,5 +1,7 @@
 import * as core from '@actions/core';
-import { installAndroidSdk } from './sdk-installer'
+import { InputOptions } from "@actions/core/lib/core";
+import { installAndroidSdk } from './sdk-installer';
+import { checkApiLevel, checkTarget, checkAbi, checkHeadless } from './input-validator';
 
 async function run() {
   try {
@@ -8,34 +10,24 @@ async function run() {
       throw new Error('This action is expected to be run within a macOS virtual machine to enable hardware acceleration.');
     }
 
-    // TODO test inputs
-    // TODO test real inputs in test.yml
-
-    // api-level is required
-    // TODO use InputOptions {true}
-    const apiLevel = core.getInput('api-level');
-    // TODO check apiLevel is number and within valid range
+    // API level of the platform and system image
+    const apiLevel = core.getInput('api-level', <InputOptions>{required: true});
+    checkApiLevel(apiLevel);
     console.log(`API level: ${apiLevel}`);
 
-    // target is optional with default
+    // target of the system image
     const target = core.getInput('target');
-    if (target !== 'default' && target !== 'google_apis') {
-      throw new Error(`Target ${target} is unknown. Please use either 'default' or 'google_apis'.`);
-    }
+    checkTarget(target);
     console.log(`target: ${target}`);
 
-    // abi is optional with default
+    // CPU / ABI of the system image
     const abi = core.getInput('abi');
-    if (abi !== 'x86' && abi !== 'x86_64') {
-      throw new Error(`abi ${abi} is unknown (ARM-based emulators are not supported). Please use either 'x86' or 'x86_64'.`);
-    }
+    checkAbi(abi);
     console.log(`cpu/abi: ${abi}`);
 
-    // headless is optional with default
+    // headless mode
     const headless = core.getInput('headless');
-    if (headless !== 'true' && headless !== 'false') {
-      throw new Error(`Input 'headless' should be either 'true' or 'false'.`);
-    }
+    checkHeadless(headless);
     console.log(`headless mode: ${headless}`);
 
     // install SDK