Coverage analysis isn't working correctly when different versions of stryker-api are mixed-and-matched

[nicojs]

Summary

Given the following directory structure:

node_modules/
└── @stryker-mutator/
    ├── core
    │     └── node_modules/@stryker-mutator/api
    └── typescript
          └── node_modules/@stryker-mutator/api

When running stryker run here, the coverage analysis perTest is broken.

Stryker config

module.exports = function(config){
  config.set({
    coverageAnalysis: 'perTest'
  });
}

Details

For some time now, @stryker-mutator/api is a direct dependency for core as well es all other plugins. The idea is that, since the api doesn't have direct side effects, it is OK to depend on it and it would be OK if the version used by a plugin is different from the core.

The api does have some class implementations, in particular File.ts. Instances of this class are serialized and deserialized using surrial.

However, this can break serialization/deserialization. The transpiler new's it's own File instances (for example, here). The File constructor class used by the plugin is unrelated to the one used in core. This makes it so it is NOT serialized as an instance of File by surrial. Later, when stryker tries to compare file content using the textContent property it never notices the changes, since it will be comparing undefined === undefined.

Workaround

The (only) workaround is to make sure that @stryker-mutator/api is hoisted to the top level of your node_modules. This should be the case when your stryker version is in sync.

node_modules/
└── @stryker-mutator/
    ├── core
    ├── typescript
    └── api

[nicojs]

This wasn't fixed after all, because of nicojs/node-surrial#9