diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 0000000..4fecb4b
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,24 @@
+# file generated with AI assistance: Claude Code - 2026-06-13 23:14:54 UTC
+name: Tests
+
+on:
+  push:
+    branches: [main, master, "feature/**"]
+  pull_request:
+
+jobs:
+  phpunit:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        php: ["8.4"]
+    name: PHPUnit (PHP ${{ matrix.php }})
+    steps:
+      - uses: actions/checkout@v4
+      - uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: none
+      - run: composer install --no-interaction --no-progress
+      - run: vendor/bin/phpunit
diff --git a/docker-compose.yml b/docker-compose.yml
new file mode 100644
index 0000000..118bccb
--- /dev/null
+++ b/docker-compose.yml
@@ -0,0 +1,15 @@
+# file generated with AI assistance: Claude Code - 2026-06-13 23:14:54 UTC
+# CLI-only test runner for this library — no MySQL/FPM required.
+# Usage (on host):
+#   docker compose run --rm php
+# Runs `composer install` then PHPUnit against tests/.
+services:
+  php:
+    build:
+      dockerfile_inline: |
+        FROM php:8.4-cli-alpine
+        COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
+    working_dir: /repo
+    volumes:
+      - .:/repo
+    command: sh -c "composer install --no-interaction --no-progress && vendor/bin/phpunit"
diff --git a/tests/Exception/ExceptionTest.php b/tests/Exception/ExceptionTest.php
new file mode 100644
index 0000000..4387538
--- /dev/null
+++ b/tests/Exception/ExceptionTest.php
@@ -0,0 +1,57 @@
+<?php
+// file generated with AI assistance: Claude Code - 2026-06-13 23:14:54 UTC
+
+declare(strict_types=1);
+
+namespace Dmstr\Bc4Client\Tests\Exception;
+
+use Dmstr\Bc4Client\Exception\Bc4ApiException;
+use Dmstr\Bc4Client\Exception\InvalidGrantException;
+use Dmstr\Bc4Client\Exception\RequestException;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Unit tests for the BC4 client exception hierarchy — verifies the type
+ * relationships callers rely on for catch-block dispatch, plus the
+ * RequestException payload accessors.
+ */
+final class ExceptionTest extends TestCase
+{
+    public function testBc4ApiExceptionIsRuntimeException(): void
+    {
+        self::assertInstanceOf(\RuntimeException::class, new Bc4ApiException('boom'));
+    }
+
+    public function testInvalidGrantExceptionExtendsBc4ApiException(): void
+    {
+        $exception = new InvalidGrantException('refresh token rejected');
+
+        self::assertInstanceOf(Bc4ApiException::class, $exception);
+        self::assertInstanceOf(\RuntimeException::class, $exception);
+        self::assertSame('refresh token rejected', $exception->getMessage());
+    }
+
+    public function testRequestExceptionExposesStatusAndBody(): void
+    {
+        $exception = new RequestException('Not Found', 404, '{"error":"missing"}');
+
+        self::assertInstanceOf(Bc4ApiException::class, $exception);
+        self::assertSame('Not Found', $exception->getMessage());
+        self::assertSame(404, $exception->getStatusCode());
+        self::assertSame('{"error":"missing"}', $exception->getResponseBody());
+        self::assertSame(0, $exception->getCode());
+    }
+
+    public function testRequestExceptionResponseBodyDefaultsToEmpty(): void
+    {
+        self::assertSame('', (new RequestException('Server Error', 500))->getResponseBody());
+    }
+
+    public function testRequestExceptionPreservesPreviousThrowable(): void
+    {
+        $previous = new \LogicException('root cause');
+        $exception = new RequestException('Bad Gateway', 502, '', $previous);
+
+        self::assertSame($previous, $exception->getPrevious());
+    }
+}