diff --git a/tests/CodeChallengeVerifiers/PlainVerifier.php b/tests/CodeChallengeVerifiers/PlainVerifier.php
new file mode 100644
index 00000000..4939c88c
--- /dev/null
+++ b/tests/CodeChallengeVerifiers/PlainVerifier.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace LeagueTests\CodeChallengeVerifiers;
+
+use League\OAuth2\Server\CodeChallengeVerifiers\PlainVerifier;
+use PHPUnit\Framework\TestCase;
+
+class PlainVerifierTest extends TestCase
+{
+    public function testGetMethod()
+    {
+        $verifier = new PlainVerifier();
+
+        $this->assertEquals('plain', $verifier->getMethod());
+    }
+
+    public function testVerifyCodeChallenge()
+    {
+        $verifier = new PlainVerifier();
+
+        $this->assertTrue($verifier->verifyCodeChallenge('foo', 'foo');
+        $this->assertFalse($verifier->verifyCodeChallenge('foo', 'bar');
+    }
+}
diff --git a/tests/CodeChallengeVerifiers/S256Verifier.php b/tests/CodeChallengeVerifiers/S256Verifier.php
new file mode 100644
index 00000000..2bf14353
--- /dev/null
+++ b/tests/CodeChallengeVerifiers/S256Verifier.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace LeagueTests\CodeChallengeVerifiers;
+
+use League\OAuth2\Server\CodeChallengeVerifiers\S256Verifier;
+use PHPUnit\Framework\TestCase;
+
+class S256Verifier extends TestCase
+{
+    public function testGetMethod()
+    {
+        $verifier = new S256Verifier();
+
+        $this->assertEquals('S256', $verifier->getMethod());
+    }
+
+    public function testVerifyCodeChallengeSucceeds()
+    {
+        $codeChallenge = $this->createCodeChallenge('foo');
+        $verifier = new S256Verifier();
+
+        $this->assertTrue($verifier->verifyCodeChallenge('foo', $codeChallenge));
+    }
+
+    public function testVerifyCodeChallengeFails()
+    {
+        $codeChallenge = $this->createCodeChallenge('bar');
+        $verifier = new S256Verifier();
+
+        $this->assertFalse($verifier->verifyCodeChallenge('foo', $codeChallenge));
+    }
+
+    private function createCodeChallenge($codeVerifier)
+    {
+        return strtr(rtrim(base64_encode(hash('sha256', $codeVerifier, true)), '='), '+/', '-_');
+    }
+}