diff --git a/src/BaseApi.php b/src/BaseApi.php
index 2cbe7c4..e9525e5 100644
--- a/src/BaseApi.php
+++ b/src/BaseApi.php
@@ -15,4 +15,15 @@ class BaseApi
     {
         $this->fetchApi = $fetchApi;
     }
+
+    protected function hasError(string $jsonResponse): bool
+    {
+        return isset(json_decode($jsonResponse, true)['errorCode']);
+    }
+
+    protected function getError(string $jsonResponse): string
+    {
+        return json_decode($jsonResponse, true)['errorDescription'];
+    }
+
 }
diff --git a/src/BilingualFile.php b/src/BilingualFile.php
index e34e7f0..2e1bba1 100644
--- a/src/BilingualFile.php
+++ b/src/BilingualFile.php
@@ -31,12 +31,17 @@ class BilingualFile extends \BrunoFontes\Memsource\BaseApi
     public function download(string $projectUid, array $jobUids, string $filename): array
     {
         $url = "/api2/v1/projects/{$projectUid}/jobs/bilingualFile";
+        $filenames = [];
 
         $groupedJobUids = array_chunk($jobUids, 100);
         for ($i = 0; $i < count($groupedJobUids); $i++) {
             $apiReadyArray = $this->_convertUidArrayToApiRequest($groupedJobUids[$i]);
             $filenames[$i] = count($groupedJobUids) > 1 ? "{$i}_{$filename}" : $filename;
             $filecontent = $this->fetchApi->fetch('jsonPost', $url, $apiReadyArray);
+            if ($this->hasError($filecontent)) {
+                $errorMsg = $this->getError($filecontent);
+                throw new \Exception("Error downloading file: {$errorMsg}", 1);
+            }
             $this->_saveIntoFile($filenames[$i], $filecontent);
         }
         return $filenames;
@@ -80,10 +85,17 @@ class BilingualFile extends \BrunoFontes\Memsource\BaseApi
     public function upload(string $filename, array $params): string
     {
         $urlParams = http_build_query($params);
-        $fileContent = file_get_contents($filename);
-        if ($fileContent === false) {
-            throw new \Exception('File for upload inexistent or invalid', 1);
+        try {
+            $fileContent = file_get_contents($filename);
+        } catch (\Exception $e) {
+            throw new \Exception('File for upload inexistent or invalid: ' . $filename, 1);
         }
-        return $this->fetchApi->fetch('put', $this->_url . "?{$urlParams}", [$fileContent]);
+
+        $response = $this->fetchApi->fetch('put', $this->_url . "?{$urlParams}", [$fileContent]);
+
+        if ($this->hasError($response)) {
+            throw new \Exception("Error uploading file {$filename}: " . $this->getError($response), 1);
+        }
+        return $response;
     }
 }
diff --git a/src/FetchApi.php b/src/FetchApi.php
index 99e4fb9..466281f 100644
--- a/src/FetchApi.php
+++ b/src/FetchApi.php
@@ -39,30 +39,44 @@ class FetchApi
         $setopt = [];
         switch ($method) {
         case 'get':
+            $this->checkAccessToken();
             $parameters = http_build_query($parameters);
             $url = $url . ($parameters ? '?'.$parameters : '');
             break;
         case 'put':
+            $this->checkAccessToken();
             $setopt = $this->getPutParam()+$this->getPostParam(implode("", $parameters));
             break;
         case 'post':
+            $this->checkAccessToken();
             $parameters = http_build_query($parameters);
             $setopt = $setopt + $this->getPostParam($parameters);
             break;
         case 'jsonPost':
+            $this->checkAccessToken();
             $setopt = $this->getJsonPostParam($parameters);
             break;
         case 'download':
+            $this->checkAccessToken();
             if (empty($filename)) {
                 throw new Exception('You need to specify a filename to download a file.', 1);
             }
             $setopt = $this->getDownloadFileParam($filename)
                     + $this->getJsonPostParam($parameters);
             break;
+        default:
+            throw new \Exception("Method {$method} is invalid on Fetch", 1);
         }
         return $this->curl($url, $setopt);
     }
 
+    private function checkAccessToken()
+    {
+        if (empty($this->token)) {
+            throw new \Exception("Missing Access Token", 1);
+        }
+    }
+
     private function getDownloadFileParam(string $filename)
     {
         return [
@@ -98,10 +112,10 @@ class FetchApi
     protected function curl(string $url, array $curl_extra_setopt = [])
     {
         if (empty($url)) {
-            throw new Exception('URL not defined', 1);
+            throw new \Exception('URL not defined', 1);
         }
 
-        $header = $this->token ? ["Authorization: Bearer {$this->token}"] : [];
+        $header = ($this->token ? ["Authorization: Bearer {$this->token}"] : []);
         $header = array_merge($header, $curl_extra_setopt[CURLOPT_HTTPHEADER]??[]);
         $curl_setopt = [
             CURLOPT_URL => $this->base_url . $url,
diff --git a/src/Jobs.php b/src/Jobs.php
index 32aa8f0..3c3cda2 100644
--- a/src/Jobs.php
+++ b/src/Jobs.php
@@ -23,6 +23,10 @@ class Jobs extends \BrunoFontes\Memsource\BaseApi
     public function list(string $projectUid, array $parameters = []): string
     {
         $url = "/api2/v2/projects/{$projectUid}/jobs";
-        return $this->fetchApi->fetch('get', $url, $parameters);
+        $response =  $this->fetchApi->fetch('get', $url, $parameters);
+        if ($this->hasError($response)) {
+            throw new \Exception("Error listing projects: " . $this->getError($response), 1);
+        }
+        return $response;
     }
 }
diff --git a/src/Project.php b/src/Project.php
index de2ed7a..cfd2def 100644
--- a/src/Project.php
+++ b/src/Project.php
@@ -21,7 +21,11 @@ class Project extends \BrunoFontes\Memsource\BaseApi
      */
     public function list(array $queryParams = []): string
     {
-        return $this->fetchApi->fetch('get', $this->_url, $queryParams);
+        $response =  $this->fetchApi->fetch('get', $this->_url, $queryParams);
+        if ($this->hasError($response)) {
+            throw new \Exception("Error listing projects: " . $this->getError($response), 1);
+        }
+        return $response;
     }
 
     /**
@@ -33,6 +37,9 @@ class Project extends \BrunoFontes\Memsource\BaseApi
      */
     public function get(string $projectUid): string
     {
-        return $this->fetchApi->fetch('get', "{$this->_url}/{$projectUid}");
+        $response = $this->fetchApi->fetch('get', "{$this->_url}/{$projectUid}");
+        if ($this->hasError($response)) {
+            throw new \Exception("Error getting project {$projectUid}: " . $this->getError($response), 1);
+        }
     }
 }
diff --git a/tests/bilingualFileTest.php b/tests/bilingualFileTest.php
new file mode 100644
index 0000000..e9d50ea
--- /dev/null
+++ b/tests/bilingualFileTest.php
@@ -0,0 +1,37 @@
+<?php
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+use BrunoFontes\Memsource;
+
+final class BilingualFileTest extends TestCase
+{
+    public function testEmptyDownloadJobUidListShouldReturnEmptyFilenames()
+    {
+        $api = new Memsource('fakeToken');
+        $this->assertEquals(
+            [],
+            $api->bilingualFile()->download('uid', [], 'filename')
+        );
+    }
+    public function testInvalidDownloadUidsShouldThrowError()
+    {
+        $api = new Memsource('fakeToken');
+        $this->expectException(\Exception::class);
+        $api->bilingualFile()->download('uid', ['a'], 'filename');
+    }
+
+    public function testUploadInexistentFileShouldThrowError()
+    {
+        $api = new Memsource('fakeToken');
+        $this->expectException(\Exception::class);
+        $api->bilingualFile()->upload('myInvalidFile', []);
+    }
+
+    public function testUploadWithNoTokenShouldThrowError()
+    {
+        $api = new Memsource('fakeToken');
+        $this->expectException(\Exception::class);
+        $api->bilingualFile()->upload('tests/bilingualFileTest.php', []);
+    }
+}
diff --git a/tests/fetchApiTest.php b/tests/fetchApiTest.php
new file mode 100644
index 0000000..5d6eb91
--- /dev/null
+++ b/tests/fetchApiTest.php
@@ -0,0 +1,57 @@
+<?php
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+use BrunoFontes\Memsource\FetchApi;
+
+final class FetchApiTest extends TestCase
+{
+    public function testEmptyFetchUrlShouldThrowError()
+    {
+        $fetch = new FetchApi('fakeToken', 'https://google.com');
+        $this->expectExceptionMessage('URL not defined');
+        $this->assertNotEmpty($fetch->fetch('get', ''));
+    }
+
+    public function testNotEmptyTokenOnFetchShouldNotThrowError()
+    {
+        $fetch = new FetchApi('fakeToken', 'https://google.com');
+        $this->assertNotEmpty($fetch->fetch('get', '/'));
+    }
+    public function testEmptyTokenOnFetchRawShouldNotThrowError()
+    {
+        $fetch = new FetchApi(null, 'http://google.com');
+        $this->assertNotEmpty($fetch->fetch('raw', '/'));
+    }
+
+    public function testEmptyTokenOnFetchGetShouldThrowError()
+    {
+        $fetch = new FetchApi(null, 'http://testUrl.com');
+        $this->expectExceptionMessage('Missing Access Token');
+        $fetch->fetch('get', 'url');
+    }
+    public function testEmptyTokenOnFetchPutShouldThrowError()
+    {
+        $fetch = new FetchApi(null, 'http://testUrl.com');
+        $this->expectExceptionMessage('Missing Access Token');
+        $fetch->fetch('put', 'url');
+    }
+    public function testEmptyTokenOnFetchPostShouldThrowError()
+    {
+        $fetch = new FetchApi(null, 'http://testUrl.com');
+        $this->expectExceptionMessage('Missing Access Token');
+        $fetch->fetch('post', 'url');
+    }
+    public function testEmptyTokenOnFetchJsonPostShouldThrowError()
+    {
+        $fetch = new FetchApi(null, 'http://testUrl.com');
+        $this->expectExceptionMessage('Missing Access Token');
+        $fetch->fetch('jsonPost', 'url');
+    }
+    public function testEmptyTokenOnFetchDownloadShouldThrowError()
+    {
+        $fetch = new FetchApi(null, 'http://testUrl.com');
+        $this->expectExceptionMessage('Missing Access Token');
+        $fetch->fetch('download', 'url');
+    }
+}
diff --git a/tests/jobsTest.php b/tests/jobsTest.php
new file mode 100644
index 0000000..ced42d1
--- /dev/null
+++ b/tests/jobsTest.php
@@ -0,0 +1,15 @@
+<?php
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+use BrunoFontes\Memsource;
+
+final class JobsTest extends TestCase
+{
+    public function testInvalidProjectUidShouldThrowError()
+    {
+        $api = new Memsource('fakeToken');
+        $this->expectException(\Exception::class);
+        $api->jobs()->list('invalidProjectUid', []);
+    }
+}
diff --git a/tests/oauthTest.php b/tests/oauthTest.php
new file mode 100644
index 0000000..4d49dac
--- /dev/null
+++ b/tests/oauthTest.php
@@ -0,0 +1,34 @@
+<?php
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+use BrunoFontes\Memsource;
+
+final class oauthTest extends TestCase
+{
+    public function testOauthGetAuthorizationCodeUrl()
+    {
+        $customServerURL = 'http://myPersonalMemsource.com';
+        $api = new Memsource(null, $customServerURL);
+        $expected = $customServerURL . '/oauth/authorize?response_type=code&client_id=id&redirect_uri=http%3A%2F%2Furi&scope=openid';
+        $memsourceUrl = $api->oauth()->getAuthorizationCodeUrl('id', 'http://uri');
+        $this->assertEquals(
+            $expected,
+            $memsourceUrl
+        );
+    }
+
+    public function testGetAccessTokenExceptionOnFakeCode()
+    {
+        $api = new Memsource();
+        $this->expectException(\Exception::class);
+        $token = $api->oauth()->getAccessToken('fakeCode', 'fakeId', 'fakePass', 'http://any');
+    }
+
+    public function testGetAccessTokenExceptionOnEmptyCode()
+    {
+        $api = new Memsource();
+        $this->expectException(\Exception::class);
+        $token = $api->oauth()->getAccessToken('', '', '', '');
+    }
+}
diff --git a/tests/projectTest.php b/tests/projectTest.php
new file mode 100644
index 0000000..cdb500e
--- /dev/null
+++ b/tests/projectTest.php
@@ -0,0 +1,21 @@
+<?php
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+use BrunoFontes\Memsource;
+
+final class ProjectTest extends TestCase
+{
+    public function testNoTokenShouldThrowError()
+    {
+        $api = new Memsource('fakeToken');
+        $this->expectException(\Exception::class);
+        $api->project()->list();
+    }
+    public function testInvalidProjectUidShouldThrowError()
+    {
+        $api = new Memsource('fakeToken');
+        $this->expectException(\Exception::class);
+        $api->project()->get('invalidProjectUid');
+    }
+}