diff --git a/composer.json b/composer.json
index 2df02cd..0822ba2 100644
--- a/composer.json
+++ b/composer.json
@@ -4,7 +4,7 @@
     "type": "library",
     "require-dev": {
         "phpunit/phpunit": "^9",
-        "giorgiosironi/eris": "^0.14.0",
+        "giorgiosironi/eris": "dev-master",
         "phpat/phpat": "^0.10",
         "facile-it/facile-coding-standard": "0.5.2",
         "vimeo/psalm": "4.30.0",
diff --git a/tests/unit/DecodersTest.php b/tests/unit/DecodersTest.php
index ec8502d..c5c4be3 100644
--- a/tests/unit/DecodersTest.php
+++ b/tests/unit/DecodersTest.php
@@ -33,6 +33,57 @@ public function testMap(): void
                 self::assertSame($i, $a->getValue());
             });
     }
+
+    public function testStringDecoder(): void
+    {
+        /** @psalm-var string $input */
+        $input = 'hello';
+
+        self::asserSuccessSameTo(
+            $input,
+            Decoders::string()->decode($input)
+        );
+    }
+
+    public function testNullDecoder(): void
+    {
+        self::asserSuccessSameTo(
+            null,
+            Decoders::null()->decode(null)
+        );
+    }
+
+    public function testMixedDecoder(): void
+    {
+        $d = Decoders::mixed();
+
+        $this
+            ->forAll(
+                Generators::oneOf(
+                    Generators::int(),
+                    Generators::string(),
+                    Generators::bool(),
+                    Generators::constant(null),
+                    Generators::tuple([
+                        'a' => Generators::int(),
+                        'b' => Generators::string(),
+                    ]),
+                    Generators::date()
+                )
+            )
+            ->then(
+                /**
+                 * @psalm-param mixed $any
+                 *
+                 * @psalm-return void
+                 *
+                 * @param mixed $any
+                 */
+                function ($any) use ($d): void {
+                    self::asserSuccessSameTo($any, $d->decode($any));
+                }
+            );
+    }
 }
 
 namespace Tests\Facile\PhpCodec\DecodersTest;