fix(test): fix mutation test not actually reading tsconfig (#1511)

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## PR Checklist

- [x] Addresses an existing open issue: fixes #1454 
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/TypeStat/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/TypeStat/blob/main/.github/CONTRIBUTING.md)
were taken

## Overview

<!-- Description of what is changed and how the code change does that.
-->

- Refactor file reading in testSetup.ts
- Fix reading tsConfig settings

Some files changed to be what they should be, and some are now exposing
bugs (`test/cases/fixes/incompleteTypes/returnTypes/expected.ts`) .

I'm not sure why the type is being removed in
`test/cases/fixes/noInferableTypes/variableDeclarations/expected.ts` but
I think this is also exposing some type. Or it may be that Map would
need some different tsconfig settings. - Filed new issue about it
#1512

.github/workflows/test-mutation.yml

@@ -4,8 +4,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: ./.github/actions/prepare
-      - run: pnpm run build --no-dts
-      - run: pnpm run test:mutation --coverage
+      - run: pnpm run test:mutation --coverage --no-file-parallelism
       - name: Codecov
         uses: codecov/codecov-action@v3
         with:

src/tests/testSetup.ts

@@ -20,20 +20,27 @@ export const runMutationTest = async (dirPath: string) => {
 		throw new Error(`${dirPath} should have a file named original.*`);
 	}
 
-	const rawTypeStatOptions = await fs.readFile(
-		path.join(dirPath, "typestat.json"),
-		{
+	const readFile = (filename: string) =>
+		fs.readFile(path.join(dirPath, filename), {
 			encoding: "utf-8",
-		},
-	);
+		});
+
+	const rawTypeStatOptions = await readFile("typestat.json");
 	const rawOptions = JSON.parse(rawTypeStatOptions) as RawTypeStatOptions;
 
 	const projectPath = path.join(dirPath, "tsconfig.json");
-	const compilerOptions: ts.CompilerOptions = (
-		ts.parseConfigFileTextToJson(projectPath, rawTypeStatOptions) as {
-			config: ts.CompilerOptions;
-		}
-	).config;
+	const rawCompilerOptionsJson = await readFile("tsconfig.json");
+	const convertResult = ts.parseConfigFileTextToJson(
+		"tsconfig.json",
+		rawCompilerOptionsJson,
+	);
+
+	if (convertResult.error) {
+		console.error(convertResult.error);
+		throw new Error("Error while reading tsconfig");
+	}
+
+	const compilerOptions = convertResult.config as ts.CompilerOptions;
 
 	const output = {
 		// eslint-disable-next-line @typescript-eslint/no-empty-function
@@ -66,7 +73,7 @@ export const runMutationTest = async (dirPath: string) => {
 		mutationsProvider: provider,
 	});
 
-	const actualContent = await fs.readFile(actualFile, { encoding: "utf-8" });
+	const actualContent = await readFile(actualFileName);
 	const expectFileName = `expected.ts${fileNameSuffix}`;
 	const expectedFilePath = path.join(dirPath, expectFileName);
 

test/cases/fixes/incompleteTypes/returnTypes/expected.ts

@@ -85,7 +85,7 @@
 		return "";
 	};
 
-	async function navigateTo(): Promise<boolean> {
+	async function navigateTo(): Promise<boolean> | boolean {
 		return await new Promise(() => "");
 	}
 

test/cases/fixes/incompleteTypes/variableTypes/expected.tsx

@@ -77,9 +77,9 @@ import * as React from "react";
 	// Async
 
 	async function _() {
-		let stringFromNullImmediate: string = await Promise.resolve<null>(null);
+		let stringFromNullImmediate: string | null = await Promise.resolve<null>(null);
 
-		let stringFromUndefinedLater: string;
+		let stringFromUndefinedLater: string | undefined;
 		stringFromUndefinedLater = await Promise.resolve<undefined>(undefined);
 	}
 

test/cases/fixes/noImplicitAny/variableDeclarations/expected.ts

@@ -92,9 +92,9 @@
 	// Async
 
 	async function _() {
-		let stringFromNullImmediate: string = await Promise.resolve<null>(null);
+		let stringFromNullImmediate: string | null = await Promise.resolve<null>(null);
 
-		let stringFromUndefinedLater: string;
+		let stringFromUndefinedLater: string | undefined;
 		stringFromUndefinedLater = await Promise.resolve<undefined>(undefined);
 	}
 

test/cases/fixes/noInferableTypes/variableDeclarations/expected.ts

@@ -86,8 +86,8 @@
 
 	// should keep their types
 	// map
-	type TypeSummariesPerNodeByName = Map<string, unknown>;
-	const incompleteTypes: TypeSummariesPerNodeByName = new Map();
+	type TypeSummariesPerNodeByName = Map<string, number>;
+	const incompleteTypes = new Map();
 	// array
 	interface Mutation {
 		readonly range: number;

test/cases/fixes/noInferableTypes/variableDeclarations/original.ts

@@ -86,7 +86,7 @@
 
 	// should keep their types
 	// map
-	type TypeSummariesPerNodeByName = Map<string, unknown>;
+	type TypeSummariesPerNodeByName = Map<string, number>;
 	const incompleteTypes: TypeSummariesPerNodeByName = new Map();
 	// array
 	interface Mutation {

test/fixMissingProperties.test.ts

@@ -11,5 +11,5 @@ describe("Missing properties", () => {
 		);
 		const { actualContent, expectedFilePath } = await runMutationTest(caseDir);
 		await expect(actualContent).toMatchFileSnapshot(expectedFilePath);
-	});
+	}, 10000);
 });