fix(typescript-checker): resolve tsconfig files correctly

In order to override options, like `noEmit: true`, the TypeScript checker tries to discover your referenced tsconfig files. It does this by parsing tsconfig and resolving the `projectReferences`. However, it always tried to resolved them from the `cwd` (with `path.resolve`).

I.e. this option overriding didn't work:

```
subdir/
├── child-a
│   └── tsconfig.json
├── child-b
│   └── tsconfig.json
└── tsconfig.json
```

Where you run Stryker with:

```json
{
  "tsconfig": "subdir/tsconfig.json"
}
```

packages/typescript-checker/src/tsconfig-helpers.ts

@@ -1,4 +1,4 @@
-import { resolve } from 'path';
+import path from 'path';
 
 import ts from 'typescript';
 import semver from 'semver';
@@ -65,10 +65,11 @@ export function overrideOptions(parsedConfig: { config?: any }, useBuildMode: bo
 /**
  * Retrieves the referenced config files based on parsed configuration
  * @param parsedConfig The parsed config file
+ * @param fromDirName The directory where to resolve from
  */
-export function retrieveReferencedProjects(parsedConfig: { config?: any }): string[] {
+export function retrieveReferencedProjects(parsedConfig: { config?: any }, fromDirName: string): string[] {
   if (Array.isArray(parsedConfig.config?.references)) {
-    return parsedConfig.config?.references.map((reference: any) => resolve(ts.resolveProjectReferencePath(reference)));
+    return parsedConfig.config?.references.map((reference: any) => path.resolve(fromDirName, ts.resolveProjectReferencePath(reference)));
   }
   return [];
 }

packages/typescript-checker/src/typescript-checker.ts

@@ -159,7 +159,7 @@ export class TypescriptChecker implements Checker {
     if (parsedConfig.error) {
       return content; // let the ts compiler deal with this error
     } else {
-      for (const referencedProject of retrieveReferencedProjects(parsedConfig)) {
+      for (const referencedProject of retrieveReferencedProjects(parsedConfig, path.dirname(fileName))) {
         this.allTSConfigFiles.add(referencedProject);
       }
       return overrideOptions(parsedConfig, buildModeEnabled);

packages/typescript-checker/test/integration/project-references.it.spec.ts

@@ -23,8 +23,7 @@ describe('Typescript checker on a project with project references', () => {
   let sut: TypescriptChecker;
 
   beforeEach(() => {
-    process.chdir(resolveTestResource());
-    testInjector.options.tsconfigFile = 'tsconfig.root.json';
+    testInjector.options.tsconfigFile = resolveTestResource('tsconfig.root.json');
     sut = testInjector.injector.injectFunction(createTypescriptChecker);
     return sut.init();
   });

packages/typescript-checker/test/integration/single-project.it.spec.ts

@@ -23,7 +23,7 @@ describe('Typescript checker on a single project', () => {
   let sut: TypescriptChecker;
 
   beforeEach(() => {
-    process.chdir(resolveTestResource());
+    testInjector.options.tsconfigFile = resolveTestResource('tsconfig.json');
     sut = testInjector.injector.injectFunction(createTypescriptChecker);
     return sut.init();
   });

packages/typescript-checker/test/integration/typescript-checkers-errors.it.spec.ts

@@ -4,7 +4,6 @@ import { testInjector } from '@stryker-mutator/test-helpers';
 import { expect } from 'chai';
 
 import { createTypescriptChecker } from '../../src';
-import { TypescriptChecker } from '../../src/typescript-checker';
 
 const resolveTestResource = (path.resolve.bind(
   path,
@@ -17,24 +16,25 @@ const resolveTestResource = (path.resolve.bind(
 ) as unknown) as typeof path.resolve;
 
 describe('Typescript checker errors', () => {
-  let sut: TypescriptChecker;
-
-  beforeEach(() => {
-    sut = testInjector.injector.injectFunction(createTypescriptChecker);
-  });
-
   it('should reject initialization if initial compilation failed', async () => {
-    process.chdir(resolveTestResource('compile-error'));
-    await expect(sut.init()).rejectedWith('TypeScript error(s) found in dry run compilation: add.ts(2,3): error TS2322:');
+    testInjector.options.tsconfigFile = resolveTestResource('compile-error', 'tsconfig.json');
+    const sut = testInjector.injector.injectFunction(createTypescriptChecker);
+    await expect(sut.init()).rejectedWith(
+      'TypeScript error(s) found in dry run compilation: testResources/errors/compile-error/add.ts(2,3): error TS2322:'
+    );
   });
 
   it('should reject initialization if tsconfig was invalid', async () => {
-    process.chdir(resolveTestResource('invalid-tsconfig'));
-    await expect(sut.init()).rejectedWith('TypeScript error(s) found in dry run compilation: tsconfig.json(1,1): error TS1005:');
+    testInjector.options.tsconfigFile = resolveTestResource('invalid-tsconfig', 'tsconfig.json');
+    const sut = testInjector.injector.injectFunction(createTypescriptChecker);
+    await expect(sut.init()).rejectedWith(
+      'TypeScript error(s) found in dry run compilation: testResources/errors/invalid-tsconfig/tsconfig.json(1,1): error TS1005:'
+    );
   });
 
   it("should reject when tsconfig file doesn't exist", async () => {
-    process.chdir(resolveTestResource('empty-dir'));
+    testInjector.options.tsconfigFile = resolveTestResource('empty-dir', 'tsconfig.json');
+    const sut = testInjector.injector.injectFunction(createTypescriptChecker);
     await expect(sut.init()).rejectedWith(
       `The tsconfig file does not exist at: "${resolveTestResource(
         'empty-dir',

packages/typescript-checker/test/unit/typescript-helpers.spec.ts

@@ -110,11 +110,15 @@ describe('typescript-helpers', () => {
 
   describe(retrieveReferencedProjects.name, () => {
     it('should result in an empty array when references are missing', () => {
-      expect(retrieveReferencedProjects({ config: { compilerOptions: {} } })).deep.eq([]);
+      expect(retrieveReferencedProjects({ config: { compilerOptions: {} } }, '')).deep.eq([]);
     });
 
     it('should retrieve referenced projects', () => {
-      expect(retrieveReferencedProjects({ config: { references: [{ path: 'some.json' }] } })).deep.eq([path.resolve('some.json')]);
+      expect(retrieveReferencedProjects({ config: { references: [{ path: 'some.json' }] } }, process.cwd())).deep.eq([path.resolve('some.json')]);
+    });
+
+    it('should resolve from given dirname', () => {
+      expect(retrieveReferencedProjects({ config: { references: [{ path: 'some.json' }] } }, 'a/b')).deep.eq([path.resolve('a', 'b', 'some.json')]);
     });
   });