Test plugin for PhpStorm

Hi, I've added some completions for my project-specific feature. Now, I'm trying to write a test for it, however it looks like neither my plugin nor PHP plugin is loaded.

class CpqHandlerCompletionTest : LightCompletionTestCase() {
    fun testCompletion() {
        configureByFile("CpqCompletionOldMethodTestData.php") // I expect to load php file here
        // but in fact, LightPlatformCodeInsightTestCase.myFile.fileType has "Plain Text" type
        complete()
    }
}

The fact that loaded file is "Plain Text" lead me to the idea, that Php plugin wasn't loaded. I tried to put some exceptions in my plugin initialisation and nothing happened (I expected test failure with my exceptions).

Can anyone guide me how to debug this issue please?