1 files changed, 70 insertions, 0 deletions
diff --git a/tests/ConstantTest.php b/tests/ConstantTest.php
new file mode 100644
index 0000000..78d1be3
--- /dev/null
+++ b/tests/ConstantTest.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake\Tests;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Zhineng\Snowflake\Constant;
+
+#[CoversClass(Constant::class)]
+final class ConstantTest extends TestCase
+{
+    public function testConstantCanBeInitialized(): void
+    {
+        $field = new Constant('machine_id', 10);
+        $this->assertSame('machine_id', $field->name);
+        $this->assertSame(10, $field->bits);
+        $this->assertSame(0, $field->value);
+    }
+
+    public function testMaxValueShouldBeCalculatedCorrectly(): void
+    {
+        $field = new Constant('machine_id', 10);
+        $maxValue = (1 << 10) - 1;
+        $this->assertSame($maxValue, $field->maxValue());
+    }
+
+    public function testInitialValueCanBeSet(): void
+    {
+        $field = new Constant('machine_id', 10, 2);
+        $this->assertSame(2, $field->value);
+    }
+
+    public function testInitialValueMustBePositive(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Field value must be non-negative.');
+        new Constant('machine_id', 10, -1);
+    }
+
+    public function testInitialValueMustNotExceedMaxValue(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Field value 1024 exceeds maximum 1023 for 10 bits.');
+        new Constant('machine_id', 10, 1024);
+    }
+
+    public function testConstantHasMakeFactoryMethod(): void
+    {
+        $field = Constant::make('machine_id', 10, 5);
+        $this->assertSame('machine_id', $field->name);
+        $this->assertSame(10, $field->bits);
+        $this->assertSame(5, $field->value);
+    }
+
+    public function testBitsMustBeAtLeastOne(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Bits must be between 1 and 63.');
+        new Constant('machine_id', 0);
+    }
+
+    public function testBitsMustNotExceed63(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Bits must be between 1 and 63.');
+        new Constant('machine_id', 64);
+    }
+}