diff --git a/composer.json b/composer.json
index 7e6f720..389876e 100644
--- a/composer.json
+++ b/composer.json
@@ -34,6 +34,12 @@
             "Curl\\": "src/Curl/"
         }
     },
+    "autoload-dev": {
+        "files": [
+            "./tests/Helper.php",
+            "./tests/User.php"
+        ]
+    },
     "config": {
         "allow-plugins": {
             "dealerdirect/phpcodesniffer-composer-installer": true
diff --git a/tests/PHPCurlClass/ContentRangeServer.php b/tests/ContentRangeServer.php
similarity index 100%
rename from tests/PHPCurlClass/ContentRangeServer.php
rename to tests/ContentRangeServer.php
diff --git a/tests/PHPCurlClass/Helper.php b/tests/Helper.php
similarity index 100%
rename from tests/PHPCurlClass/Helper.php
rename to tests/Helper.php
diff --git a/tests/PHPCurlClass/PHPCurlClassTest.php b/tests/PHPCurlClass/PHPCurlClassTest.php
index 087351a..5014b42 100644
--- a/tests/PHPCurlClass/PHPCurlClassTest.php
+++ b/tests/PHPCurlClass/PHPCurlClassTest.php
@@ -8,7 +8,7 @@ use Curl\Url;
 use Helper\Test;
 use Helper\User;
 
-class CurlTest extends \PHPUnit\Framework\TestCase
+class PHPCurlClassTest extends \PHPUnit\Framework\TestCase
 {
     private $skip_slow_tests;
 
@@ -98,8 +98,8 @@ class CurlTest extends \PHPUnit\Framework\TestCase
 
         $test = new Test();
         $user_agent = $test->server('server', 'GET', ['key' => 'HTTP_USER_AGENT']);
-        $this->assertRegExp('/' . $php_version . '/', $user_agent);
-        $this->assertRegExp('/' . $curl_version . '/', $user_agent);
+        $this->assertMatchesRegularExpression('/' . $php_version . '/', $user_agent);
+        $this->assertMatchesRegularExpression('/' . $curl_version . '/', $user_agent);
     }
 
     public function testGet()
@@ -3092,6 +3092,7 @@ class CurlTest extends \PHPUnit\Framework\TestCase
     }
 
     /**
+     * @requires PHPUnit < 10
      * @expectedException \PHPUnit\Framework\Error\Warning
      */
     public function testRequiredOptionCurlOptReturnTransferEmitsWarning()
@@ -3102,6 +3103,23 @@ class CurlTest extends \PHPUnit\Framework\TestCase
         $curl->setOpt(CURLOPT_RETURNTRANSFER, false);
     }
 
+    /**
+     * @requires PHPUnit >= 10
+     */
+    public function testRequiredOptionCurlOptReturnTransferEmitsWarningPHPUnit10Plus()
+    {
+        set_error_handler(static function (int $errno, string $errstr): never {
+            throw new \Exception($errstr, $errno);
+        }, E_USER_WARNING);
+
+        $this->expectExceptionMessage('CURLOPT_RETURNTRANSFER is a required option');
+
+        $curl = new Curl();
+        $curl->setOpt(CURLOPT_RETURNTRANSFER, false);
+
+        restore_error_handler();
+    }
+
     public function testRequestMethodSuccessiveGetRequests()
     {
         $test = new Test();
diff --git a/tests/PHPCurlClass/PHPMultiCurlClassTest.php b/tests/PHPCurlClass/PHPMultiCurlClassTest.php
index 0260e39..d4a008a 100644
--- a/tests/PHPCurlClass/PHPMultiCurlClassTest.php
+++ b/tests/PHPCurlClass/PHPMultiCurlClassTest.php
@@ -6,7 +6,7 @@ use Curl\Curl;
 use Curl\MultiCurl;
 use Helper\Test;
 
-class MultiCurlTest extends \PHPUnit\Framework\TestCase
+class PHPMultiCurlClassTest extends \PHPUnit\Framework\TestCase
 {
     private $skip_slow_tests;
 
diff --git a/tests/PHPCurlClass/RangeHeader.php b/tests/RangeHeader.php
similarity index 100%
rename from tests/PHPCurlClass/RangeHeader.php
rename to tests/RangeHeader.php
diff --git a/tests/PHPCurlClass/User.php b/tests/User.php
similarity index 100%
rename from tests/PHPCurlClass/User.php
rename to tests/User.php
diff --git a/tests/ci.sh b/tests/ci.sh
index 9a2d4f3..bb6f0cf 100755
--- a/tests/ci.sh
+++ b/tests/ci.sh
@@ -1,6 +1,8 @@
+#!/usr/bin/env bash
+
 remove_expectWarning() {
     # Fix "Call to undefined method CurlTest\CurlTest::expectWarning()".
-    sed -i'' -e"/->expectWarning(/d" "./PHPCurlClass/PHP"*
+    sed -i$(sed v < /dev/null 2> /dev/null || echo -n " ''") -e "/->expectWarning(/d" "./PHPCurlClass/PHP"*
 }
 
 replace_assertStringContainsString() {
@@ -8,19 +10,38 @@ replace_assertStringContainsString() {
     # +->assertContains(
     find='->assertStringContainsString('
     replace='->assertContains('
-    sed -i'' -e"s/${find}/${replace}/" "./PHPCurlClass/PHP"*
+    sed -i$(sed v < /dev/null 2> /dev/null || echo -n " ''") -e "s/${find}/${replace}/" "./PHPCurlClass/PHP"*
+}
+
+replace_assertMatchesRegularExpression() {
+    # -->assertMatchesRegularExpression(
+    # +->assertRegExp(
+    find='->assertMatchesRegularExpression('
+    replace='->assertRegExp('
+    sed -i$(sed v < /dev/null 2> /dev/null || echo -n " ''") -e"s/${find}/${replace}/" "./PHPCurlClass/PHP"*
 }
 
 phpunit_v6_5_shim() {
     remove_expectWarning
+    replace_assertMatchesRegularExpression
     replace_assertStringContainsString
 }
 
 phpunit_v7_5_shim() {
     remove_expectWarning
+    replace_assertMatchesRegularExpression
 }
 
-phpunit_v8_1_shim() {
+phpunit_v8_5_shim() {
+    remove_expectWarning
+    replace_assertMatchesRegularExpression
+}
+
+phpunit_v9_shim() {
+    replace_assertMatchesRegularExpression
+}
+
+phpunit_v10_shim() {
     remove_expectWarning
 }
 
@@ -59,7 +80,7 @@ for i in $(seq 0 $(("${server_count}" - 1))); do
     port=8000
     (( port += $i ))
 
-    php -S "127.0.0.1:${port}" -t PHPCurlClass/ &> /dev/null &
+    php -S "127.0.0.1:${port}" server.php &> /dev/null &
     pids["${i}"]="${!}"
 done
 
@@ -77,12 +98,22 @@ fi
 phpunit_version="$("${phpunit_to_use}" --version | grep -Eo "[0-9]+\.[0-9]+\.[0-9]+")"
 echo "phpunit_version: ${phpunit_version}"
 
+extra_args="${@}"
 if [[ "${phpunit_version}" == "6.5."* ]]; then
     phpunit_v6_5_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
 elif [[ "${phpunit_version}" == "7.5."* ]]; then
     phpunit_v7_5_shim
-elif [[ "${phpunit_version}" == "8.1."* ]]; then
-    phpunit_v8_1_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
+elif [[ "${phpunit_version}" == "8.5."* ]]; then
+    phpunit_v8_5_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
+elif [[ "${phpunit_version}" == "9."* ]]; then
+    phpunit_v9_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
+elif [[ "${phpunit_version}" == "10."* ]]; then
+    phpunit_v10_shim
+    phpunit_args=" --display-incomplete --display-skipped --display-deprecations --display-errors --display-notices --display-warnings --fail-on-risky ${extra_args}"
 fi
 
 if [[ "${CI_PHP_VERSION}" == "7.0" ]]; then
@@ -92,7 +123,8 @@ fi
 # Run tests.
 "${phpunit_to_use}" --version
 "${phpunit_to_use}" \
-    --configuration "phpunit.xml"
+    --configuration "phpunit.xml" \
+    ${phpunit_args}
 if [[ "${?}" -ne 0 ]]; then
     echo "Error: phpunit command failed"
     errors+=("phpunit command failed")
diff --git a/tests/PHPCurlClass/index.php b/tests/index.php
similarity index 100%
rename from tests/PHPCurlClass/index.php
rename to tests/index.php
diff --git a/tests/phpunit.xml b/tests/phpunit.xml
index 87b3ee1..ea668de 100644
--- a/tests/phpunit.xml
+++ b/tests/phpunit.xml
@@ -1,7 +1,7 @@
 <phpunit bootstrap="../vendor/autoload.php" colors="true">
     <testsuites>
         <testsuite name="PHPCurlClass">
-            <directory suffix=".php">./PHPCurlClass/</directory>
+            <directory suffix="Test.php">../tests/</directory>
         </testsuite>
     </testsuites>
     <php>
diff --git a/tests/run.sh b/tests/run.sh
index d1e3b8d..d3745cd 100755
--- a/tests/run.sh
+++ b/tests/run.sh
@@ -2,7 +2,7 @@
 
 remove_expectWarning() {
     # Fix "Call to undefined method CurlTest\CurlTest::expectWarning()".
-    sed -i'' -e"/->expectWarning(/d" "./PHPCurlClass/PHP"*
+    sed -i$(sed v < /dev/null 2> /dev/null || echo -n " ''") -e "/->expectWarning(/d" "./PHPCurlClass/PHP"*
 }
 
 replace_assertStringContainsString() {
@@ -10,19 +10,38 @@ replace_assertStringContainsString() {
     # +->assertContains(
     find='->assertStringContainsString('
     replace='->assertContains('
-    sed -i'' -e"s/${find}/${replace}/" "./PHPCurlClass/PHP"*
+    sed -i$(sed v < /dev/null 2> /dev/null || echo -n " ''") -e "s/${find}/${replace}/" "./PHPCurlClass/PHP"*
+}
+
+replace_assertMatchesRegularExpression() {
+    # -->assertMatchesRegularExpression(
+    # +->assertRegExp(
+    find='->assertMatchesRegularExpression('
+    replace='->assertRegExp('
+    sed -i$(sed v < /dev/null 2> /dev/null || echo -n " ''") -e"s/${find}/${replace}/" "./PHPCurlClass/PHP"*
 }
 
 phpunit_v6_5_shim() {
     remove_expectWarning
+    replace_assertMatchesRegularExpression
     replace_assertStringContainsString
 }
 
 phpunit_v7_5_shim() {
     remove_expectWarning
+    replace_assertMatchesRegularExpression
 }
 
-phpunit_v8_1_shim() {
+phpunit_v8_5_shim() {
+    remove_expectWarning
+    replace_assertMatchesRegularExpression
+}
+
+phpunit_v9_shim() {
+    replace_assertMatchesRegularExpression
+}
+
+phpunit_v10_shim() {
     remove_expectWarning
 }
 
@@ -58,7 +77,7 @@ for i in $(seq 0 $(("${server_count}" - 1))); do
     port=8000
     (( port += $i ))
 
-    php -S "127.0.0.1:${port}" -t PHPCurlClass/ &> /dev/null &
+    php -S "127.0.0.1:${port}" server.php &> /dev/null &
     pids["${i}"]="${!}"
 done
 
@@ -76,12 +95,22 @@ fi
 phpunit_version="$("${phpunit_to_use}" --version | grep -Eo "[0-9]+\.[0-9]+\.[0-9]+")"
 echo "phpunit_version: ${phpunit_version}"
 
+extra_args="${@}"
 if [[ "${phpunit_version}" == "6.5."* ]]; then
     phpunit_v6_5_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
 elif [[ "${phpunit_version}" == "7.5."* ]]; then
     phpunit_v7_5_shim
-elif [[ "${phpunit_version}" == "8.1."* ]]; then
-    phpunit_v8_1_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
+elif [[ "${phpunit_version}" == "8.5."* ]]; then
+    phpunit_v8_5_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
+elif [[ "${phpunit_version}" == "9."* ]]; then
+    phpunit_v9_shim
+    phpunit_args=" --debug --verbose --fail-on-risky ${extra_args}"
+elif [[ "${phpunit_version}" == "10."* ]]; then
+    phpunit_v10_shim
+    phpunit_args=" --display-incomplete --display-skipped --display-deprecations --display-errors --display-notices --display-warnings --fail-on-risky ${extra_args}"
 fi
 
 if [[ "${CI_PHP_VERSION}" == "7.0" ]]; then
@@ -89,11 +118,10 @@ if [[ "${CI_PHP_VERSION}" == "7.0" ]]; then
 fi
 
 # Run tests.
-extra_args="${@}"
 "${phpunit_to_use}" --version
 "${phpunit_to_use}" \
     --configuration "phpunit.xml" \
-    ${extra_args}
+    ${phpunit_args}
 if [[ "${?}" -ne 0 ]]; then
     echo "Error: phpunit command failed"
     errors+=("phpunit command failed")
diff --git a/tests/PHPCurlClass/server.php b/tests/server.php
similarity index 99%
rename from tests/PHPCurlClass/server.php
rename to tests/server.php
index 85bf66f..4f1443a 100644
--- a/tests/PHPCurlClass/server.php
+++ b/tests/server.php
@@ -11,8 +11,6 @@ require_once 'ContentRangeServer.php';
 require_once 'RangeHeader.php';
 require_once 'Helper.php';
 
-use Helper\Test;
-
 $http_raw_post_data = file_get_contents('php://input');
 $_PUT = [];
 $_PATCH = [];
@@ -146,12 +144,12 @@ if ($test === 'http_basic_auth') {
     ]);
     exit;
 } elseif ($test === 'post_file_path_upload') {
-    echo Helper\mime_type($_FILES[$key]['tmp_name']);
+    echo \Helper\mime_type($_FILES[$key]['tmp_name']);
     exit;
 } elseif ($test === 'put_file_handle') {
     $tmp_filename = tempnam('/tmp', 'php-curl-class.');
     file_put_contents($tmp_filename, $http_raw_post_data);
-    echo Helper\mime_type($tmp_filename);
+    echo \Helper\mime_type($tmp_filename);
     unlink($tmp_filename);
     exit;
 } elseif ($test === 'request_method') {