Light weight integration tests

[firelizzard18]

Would you (the Go team) be interested in (a PR) implementing integration tests that can be run directly, without spawning an instance of VSCode? The GitLab extension does this by creating a partial mock of the vscode package.

[firelizzard18]

/cc @hyangah

[hyangah]

What do you think about typemoq? I saw python extension and other extensions using it
For example: https://github.com/microsoft/vscode-python/search?q=typemoq

[firelizzard18]

My goal is to allow (some) tests to be run without launching VSCode. Since vscode is normally provided by VSCode/the extension host, to allow tests to be run independently, we have to intercept require('vscode'). The only test framework I know of that supports intercepting require is Jest. I skimmed typemoq's readme and I didn't see anything about require or import. I don't have any objections to sinon as a mocking framework (nor any objections to typemoq).

I played with an number of existing solutions for intercepting require. I think the simplest solution is to do what mock-require does: replace Module._load (from this WIP CL):

import Module = require('module');

const { _load } = Module;

Module._load = function (request: string, parent?: Module, ...rest: any[]) {
	switch (request) {
		case 'vscode':
			return require('./mocks/MockVSCode');
		default:
			return _load.call(this, request, parent, ...rest);
	}
};

require('./integration/index').run();

This intercepts require('vscode') and replaces it with whatever code we want. The implementation is straight forward and easy to extend (we might want to intercept vscode-languageclient).

However, there is an issue with respect to minimizing the mock vscode: The import graph of/between files in src is quite interdependent/tangled, and as a result, goMain is almost always imported, no matter what you start with. If we want to go down this path, I recommend simplifying the intra-src import graph, so we don't need to create mocks for features that aren't tested.

For example, if I want to test GoTestResolver, I hit the following import chain

• goTest/resolve
• goStatus
• goEnvironmentStatus
• goEnv
• util
• goLanguageServer
• goCodeAction
• goImport
• goInstallTools
• goMain

goMain effectively loads the entire extension, which means everything the extension uses anywhere must be mocked. Additionally, loading goStatus requires mocking OutputChannel and StatusBarItem, and loading goLanguageServer requires intercepting vscode-languageclient. Alternatively, we could add a mechanism to intercept arbitrary modules (or just use mock-require or proxyquire) and use that to mock require('./goStatus').