diff --git a/tests/IntRangeTest.php b/tests/IntRangeTest.php
index 1f78215..9c13964 100644
--- a/tests/IntRangeTest.php
+++ b/tests/IntRangeTest.php
@@ -7,7 +7,7 @@
 
 final class IntRangeTest extends TestCase
 {
-    public function testSerializeThrowsIfNotAnInt(): void
+    public function testSerializeThrowsIfString(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $this->expectExceptionMessage('Value not in range 1-12: "12".');
@@ -15,7 +15,15 @@ public function testSerializeThrowsIfNotAnInt(): void
         (new UpToADozen())->serialize('12');
     }
 
-    public function testSerializeThrowsIfInvalid(): void
+    public function testSerializeThrowsIfFloat(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Value not in range 1-12: 5.43.');
+
+        (new UpToADozen())->serialize(5.43);
+    }
+
+    public function testSerializeThrowsIfTooHigh(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $this->expectExceptionMessage('Value not in range 1-12: 13.');
@@ -23,14 +31,39 @@ public function testSerializeThrowsIfInvalid(): void
         (new UpToADozen())->serialize(13);
     }
 
-    public function testSerializePassesWhenValid(): void
+    public function testSerializeThrowsIfZero(): void
     {
-        $serializedResult = (new UpToADozen())->serialize(12);
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Value not in range 1-12: 0.');
 
-        self::assertSame(12, $serializedResult);
+        (new UpToADozen())->serialize(0);
     }
 
-    public function testParseValueThrowsIfInvalid(): void
+    public function testSerializeThrowsIfTooLow(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Value not in range 1-12: -1.');
+
+        (new UpToADozen())->serialize(-1);
+    }
+
+    public function testSerializePassesWithHighest(): void
+    {
+        self::assertSame(
+            12,
+            (new UpToADozen())->serialize(12)
+        );
+    }
+
+    public function testSerializePassesWithLowest(): void
+    {
+        self::assertSame(
+            1,
+            (new UpToADozen())->serialize(1)
+        );
+    }
+
+    public function testParseValueThrowsIfTooHigh(): void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Value not in range 1-12: 13.');
@@ -38,11 +71,35 @@ public function testParseValueThrowsIfInvalid(): void
         (new UpToADozen())->parseValue(13);
     }
 
-    public function testParseValuePassesIfValid(): void
+    public function testParseValueThrowsIfZero(): void
+    {
+        $this->expectException(Error::class);
+        $this->expectExceptionMessage('Value not in range 1-12: 0.');
+
+        (new UpToADozen())->parseValue(0);
+    }
+
+    public function testParseValueThrowsIfTooLow(): void
+    {
+        $this->expectException(Error::class);
+        $this->expectExceptionMessage('Value not in range 1-12: -1.');
+
+        (new UpToADozen())->parseValue(-1);
+    }
+
+    public function testParseValuePassesWithHighest(): void
     {
         self::assertSame(
             12,
             (new UpToADozen())->parseValue(12)
         );
     }
+
+    public function testParseValuePassesWithLowest(): void
+    {
+        self::assertSame(
+            1,
+            (new UpToADozen())->parseValue(1)
+        );
+    }
 }