Add dedicated exception tests and include Exception dir in coverage

Exception classes had no direct tests, so their inheritance chain,
message propagation, and newly added classes (InvalidTemplateSyntaxException,
InvalidTemplateVariableNameException) were unverified. ExceptionTest covers
all exception classes for correct base-class inheritance and message
preservation. Also remove the src/Exception coverage exclusion from
phpunit.xml so exception code is now tracked in the coverage report.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: aymanrb

phpunit.xml

@@ -14,8 +14,5 @@
         <include>
             <directory suffix=".php">src</directory>
         </include>
-        <exclude>
-            <directory suffix=".php">src/Exception</directory>
-        </exclude>
     </source>
 </phpunit>

tests/Exception/ExceptionTest.php

@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace aymanrb\UnstructuredTextParser\Tests\Exception;
+
+use aymanrb\UnstructuredTextParser\Exception\InvalidParsedDataKeyException;
+use aymanrb\UnstructuredTextParser\Exception\InvalidParseFileException;
+use aymanrb\UnstructuredTextParser\Exception\InvalidTemplateSyntaxException;
+use aymanrb\UnstructuredTextParser\Exception\InvalidTemplatesDirectoryException;
+use aymanrb\UnstructuredTextParser\Exception\InvalidTemplateVariableNameException;
+use aymanrb\UnstructuredTextParser\Exception\UnstructuredTextParserException;
+use PHPUnit\Framework\TestCase;
+
+class ExceptionTest extends TestCase
+{
+    public function testAllExceptionsExtendBaseException(): void
+    {
+        $this->assertInstanceOf(UnstructuredTextParserException::class, new InvalidParseFileException());
+        $this->assertInstanceOf(UnstructuredTextParserException::class, new InvalidParsedDataKeyException());
+        $this->assertInstanceOf(UnstructuredTextParserException::class, new InvalidTemplatesDirectoryException());
+        $this->assertInstanceOf(UnstructuredTextParserException::class, new InvalidTemplateSyntaxException());
+        $this->assertInstanceOf(UnstructuredTextParserException::class, new InvalidTemplateVariableNameException());
+    }
+
+    public function testBaseExceptionExtendsRuntimeException(): void
+    {
+        $this->assertInstanceOf(\Exception::class, new UnstructuredTextParserException());
+    }
+
+    public function testInvalidTemplatesDirectoryExceptionPreservesMessage(): void
+    {
+        $message = 'Invalid templates directory provided';
+        $exception = new InvalidTemplatesDirectoryException($message);
+
+        $this->assertSame($message, $exception->getMessage());
+    }
+
+    public function testInvalidParseFileExceptionPreservesMessage(): void
+    {
+        $path = '/some/missing/file.txt';
+        $exception = new InvalidParseFileException($path);
+
+        $this->assertSame($path, $exception->getMessage());
+    }
+
+    public function testInvalidParsedDataKeyExceptionPreservesMessage(): void
+    {
+        $message = 'Undefined results key: myKey';
+        $exception = new InvalidParsedDataKeyException($message);
+
+        $this->assertSame($message, $exception->getMessage());
+    }
+
+    public function testInvalidTemplateSyntaxExceptionPreservesMessage(): void
+    {
+        $message = 'Template produced an invalid regex pattern: No error';
+        $exception = new InvalidTemplateSyntaxException($message);
+
+        $this->assertSame($message, $exception->getMessage());
+    }
+
+    public function testInvalidTemplateVariableNameExceptionPreservesMessage(): void
+    {
+        $message = 'Invalid template variable name "my-var"';
+        $exception = new InvalidTemplateVariableNameException($message);
+
+        $this->assertSame($message, $exception->getMessage());
+    }
+}