tests: start replacing jest with mocha, starting with unit-cli

[connorjclark]

• Use mocha instead of jest for test runner, this PR is just the unit-cli tests
• Still using Jest mocks via jest-mock. Package works independent of the Jest test runner
• Also, still using Jest snapshots via jest-snapshot. Set SNAPSHOT_UPDATE=1 to update snapshots
• Use testdouble to replace es module imports (with the jest mocks)
• mocha-setup.js does two things: 1) sets global.expect 2) configures the mocha test runner to use jest-snapshot
• Need to confirm coverage works

[connorjclark]

with jest import yargs from 'yargs here and in the test file results in yargs.getGroups() working in the test file. That function is added to the module dynamically after being called, which is why this test did this seemingly no-op call to getFlags.

But, that property is only added to the module object in jest because ... reasons? The modules aren't really es modules, I guess, and es module objects are read-only, IIRC.

Anyhow, the getGroups method is also added to the yargs parser object, so to get to that I split up the implementation across two functions.

[connorjclark]

Mocha does global.before, jest does global.beforeAll. To make transition slightly easier, I thought having the same interface for some parts would be helpful.

[connorjclark]

There's no timeout parameter for mocha hook functions, but there is for jest lifecycle functions.

[connorjclark]

There's some type collisions here inside node_modules (across globals declared by jest and mocha) that I need help dealing with.

[connorjclark]

patch-package could work, just deleting the lines that declare the global vars in mocha (and relying on the mocha-setup to coerce the jest-defined interface and use the mocha functions there)

I think this is unavoidable, unless we make the switch to mocha in one giant PR.

cypress-io/cypress#6690 (comment)

[brendankenny]

is the problem that we have jest and mocha tests in the same namespace? We could use project references to split cli unit tests up in that case. Or is using jest-mock/snapshots/expect enough to clash with the mocha types?

[connorjclark]

They both do toplevel declare var, so the global namespace.

I don't see how project references would resolve it–rather, I don't know enough about using projects in TS to know how it'd solve things.

[brendankenny]

const {describe, it} = require('mocha') works (though the globals still exist), so we could also convert to using actual imports rather than the terrible global thing all these test runners do. This person apparently keeps a fork of @types/mocha but with only local declarations: mochajs/mocha#956 (comment) 🤷

But it might just be easier to use project references.

I don't see how project references would resolve it–rather, I don't know enough about using projects in TS to know how it'd solve things.

Really they wouldn't even be project references here, it would just be a different tsconfig which doesn't include the jest types (or the mocha types, depending on where we put it). This is the same as e.g. the treemap tsconfig, where we only include the tabulator-tables types from node_modules, and exclude all the other types (like we don't want any of the @types/node globals muddying up code suggestions in code that's only going to run in the browser):

lighthouse/treemap/tsconfig.json

Lines 8 to 9 in 82772f9

	// Selectively include types from node_modules/.
	"types": ["tabulator-tables"],

FWIW projects references are just that, multiple tsconfigs, with the addition of the references section where one tsconfig can reference another as a type dependency, e.g. treemap pulling in '../report/' as a dependency in the exact same way it's pulling in tabulator-tables as one. It's much more analogous to our multiple eslintrc files than yarn/npm workspaces or lerna or whatever.

[connorjclark]

I've run into complications with this approach because referencing files outside of a tsconfig project is not allowed.

diff --git a/lighthouse-cli/test/cli/mocha-globals.d.ts b/lighthouse-cli/test/cli/mocha-globals.d.ts
new file mode 100644
index 000000000..23f979f1f
--- /dev/null
+++ b/lighthouse-cli/test/cli/mocha-globals.d.ts
@@ -0,0 +1,5 @@
+import expect_ from 'expect';
+
+declare global {
+  const expect: typeof expect_;
+}
diff --git a/lighthouse-cli/test/cli/tsconfig.json b/lighthouse-cli/test/cli/tsconfig.json
new file mode 100644
index 000000000..88fce8081
--- /dev/null
+++ b/lighthouse-cli/test/cli/tsconfig.json
@@ -0,0 +1,15 @@
+{
+  "extends": "../../../tsconfig-base.json",
+  "compilerOptions": {
+    // "rootDir": "../../..",
+    // "outDir": "../../../.tmp/tsbuildinfo/cli-tests",
+    // Selectively include types from node_modules/.
+    "types": ["tabulator-tables", "mocha"],
+  },
+  "include": [
+    "**/*.js",
+    "mocha-globals.d.ts",
+    "../../../types/global-lh.d.ts",
+    // "../../../**/*.js"
+  ],
+}

[connorjclark]

@paulirish

quibble

That is part of the testdouble module replacing library. https://github.com/testdouble/quibble