Manual invalidation feature (#74)

* test: isolate feature #73

* feature: manual invalidation
closes #73

Author: g105b

src/Cache.php

@@ -40,6 +40,10 @@ public function get(
 		}
 	}
 
+	public function invalidate(string $name):void {
+		$this->fileAccess->invalidate($name);
+	}
+
 	public function getString(string $name, callable $callback):string {
 		return (string)$this->get($name, $callback);
 	}

test/phpunit/CacheTest.php

@@ -93,6 +93,23 @@ public function testGet_urlName_doesNotTraverseFilesystem():void {
 		self::assertFileDoesNotExist(sys_get_temp_dir() . "/outside-cache");
 	}
 
+	public function testInvalidate_removesSingleCacheByKey():void {
+		$sut = $this->getSut();
+		$name = "invalidate-me";
+		$value = "cached-value";
+
+		self::assertSame($value, $sut->get($name, fn() => $value));
+
+		$expectedFile = sys_get_temp_dir()
+			. "/phpgt-filecache/"
+			. rawurlencode($name);
+		self::assertFileExists($expectedFile);
+
+		$sut->invalidate($name);
+
+		self::assertFileDoesNotExist($expectedFile);
+	}
+
 	public function testGet_generationExceptionDoesNotWriteInvalidValue():void {
 		$fileAccess = self::createMock(FileAccess::class);
 		$fileAccess->expects(self::once())