[policy] Isolate CI base fallback tests

Change-Id: I16ef1f0a809511a622bd1c0ef1d7f594360164c6

Author: heimanba

scripts/verify.test.ts

@@ -43,18 +43,11 @@ describe("verification profiles", () => {
 	});
 
 	test("rejects an explicit BASE that is not a commit", () => {
-		expect(() => resolveComparisonBase("not-a-real-commit")).toThrow("is not a commit");
+		expect(() => resolveComparisonBase("not-a-real-commit", false)).toThrow("is not a commit");
 	});
 
 	test("falls back when a push base disappeared after a GitHub history rewrite", () => {
-		const previous = process.env.GITHUB_ACTIONS;
-		process.env.GITHUB_ACTIONS = "true";
-		try {
-			expect(resolveComparisonBase("not-a-real-commit")).toBeTruthy();
-		} finally {
-			if (previous === undefined) delete process.env.GITHUB_ACTIONS;
-			else process.env.GITHUB_ACTIONS = previous;
-		}
+		expect(resolveComparisonBase("not-a-real-commit", true)).toBeTruthy();
 	});
 });
 

scripts/verify.ts

@@ -52,10 +52,13 @@ function gitCommitExists(ref: string): boolean {
 	return Bun.spawnSync(["git", "cat-file", "-e", `${ref}^{commit}`], { cwd: root, stderr: "ignore" }).exitCode === 0;
 }
 
-export function resolveComparisonBase(explicitBase = process.env.BASE): string | undefined {
+export function resolveComparisonBase(
+	explicitBase = process.env.BASE,
+	allowMissingExplicitBase = process.env.GITHUB_ACTIONS === "true",
+): string | undefined {
 	if (explicitBase && !/^0+$/.test(explicitBase)) {
 		if (gitCommitExists(explicitBase)) return explicitBase;
-		if (process.env.GITHUB_ACTIONS !== "true") {
+		if (!allowMissingExplicitBase) {
 			throw new Error(`Verification BASE '${explicitBase}' is not a commit.`);
 		}
 		console.warn(`Verification BASE '${explicitBase}' is unavailable after a history rewrite; using a local fallback.`);