Started basic unit tests

Author: olivertappin

phpunit.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit backupGlobals="false"
+         backupStaticAttributes="false"
+         bootstrap="vendor/autoload.php"
+         colors="true"
+         convertErrorsToExceptions="true"
+         convertNoticesToExceptions="true"
+         convertWarningsToExceptions="true"
+         processIsolation="false"
+         stopOnFailure="false"
+>
+    <testsuites>
+        <testsuite name="Package Test Suite">
+            <directory suffix=".php">./tests/</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>

tests/Filter/Rule/FileRuleTest.php

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+<?php
+
+namespace PhpcsDiff\Tests\Filter\Rule;
+
+use PhpcsDiff\Filter\Rule\Exception\InvalidArgumentException;
+use PhpcsDiff\Filter\Rule\Exception\RuntimeException;
+use PhpcsDiff\Filter\Rule\FileRule;
+use PhpcsDiff\Tests\TestBase;
+
+class FileRuleTest extends TestBase
+{
+    /**
+     * @covers FileRule::__invoke
+     */
+    public function testInvoke()
+    {
+        $rule = new FileRule();
+
+        $this->assertException(InvalidArgumentException::class, function() use ($rule) {
+            $rule(null);
+        });
+
+        $this->assertException(RuntimeException::class, function() use ($rule) {
+            $rule('');
+        });
+
+        mkdir('test');
+
+        $this->assertException(RuntimeException::class, function() use ($rule) {
+            $rule('test');
+        });
+
+        rmdir('test');
+
+
+
+//
+//        $handle = fopen('test', 'wb');
+//
+//        $this->assertException(RuntimeException::class, function() use ($rule) {
+//            $rule('');
+//        });
+//
+//        fclose($handle);
+    }
+
+    /**
+     * @expectedException InvalidArgumentException
+     * @expectedExceptionMessage The data argument provided is not a string.
+     * @throws \PhpcsDiff\Filter\Rule\Exception\RuleException
+     */
+    public function testNonString()
+    {
+        $rule = new FileRule();
+        $rule(null);
+    }
+}

tests/FilterTest.php

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+<?php
+
+namespace PhpcsDiff\Tests;
+
+use PHPUnit\Framework\TestCase;
+
+abstract class TestBase extends TestCase
+{
+    /**
+     * @param string $expectClass
+     * @param callable $callback
+     */
+    protected function assertException($expectClass, callable $callback)
+    {
+        try {
+            $callback();
+        } catch (\Throwable $exception) {
+            $this->assertInstanceOf($expectClass, $exception, 'An invalid exception was thrown');
+            return;
+        }
+
+        $this->fail('No exception was thrown');
+    }
+}