test(jest-runner): keep corpus lookup off tmp parents

Mock the parent directory walk for the missing package.json
case so the corpus test stays independent of tmp
ancestors on the local machine.

Type the readdirSync mock explicitly so TypeScript
keeps compiling the test.

Author: oetr

packages/jest-runner/corpus.test.ts

@@ -95,7 +95,28 @@ describe("Corpus", () => {
 
 		it("throw error if no package.json was found", () => {
 			const fuzzTest = mockFuzzTest({ generatePackageJson: false });
-			expect(() => new Corpus(fuzzTest, [])).toThrow();
+			const originalReaddirSync = (directoryPath: fs.PathLike): string[] =>
+				fs.readdirSync(directoryPath);
+			const readdirSync = jest.spyOn(fs, "readdirSync");
+			readdirSync.mockImplementation(((directoryPath: fs.PathLike) => {
+				if (typeof directoryPath === "string") {
+					const fuzzTestDir = path.dirname(fuzzTest);
+					if (
+						directoryPath === fuzzTestDir ||
+						directoryPath === path.dirname(fuzzTestDir) ||
+						directoryPath === path.parse(fuzzTestDir).root
+					) {
+						return [];
+					}
+				}
+				return originalReaddirSync(directoryPath);
+			}) as unknown as typeof fs.readdirSync);
+
+			try {
+				expect(() => new Corpus(fuzzTest, [])).toThrow();
+			} finally {
+				readdirSync.mockRestore();
+			}
 		});
 	});
 });