test(spec): cover fluent value generators determinism and chaining

pkg/spec/test/values.test.ts

@@ -0,0 +1,75 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { Pcg } from "../src/pcg.ts";
+import { setSamplerRng } from "../src/sampler-rng.ts";
+import { edgeCaseText, emails, integers, strings } from "../src/values.ts";
+import { INPUT_CORPUS } from "../src/corpus.ts";
+import type { Sampler } from "../src/types.ts";
+
+function withRng<T>(seed: bigint, body: () => T): T {
+  setSamplerRng(new Pcg(seed, 0n));
+  try {
+    return body();
+  } finally {
+    setSamplerRng(null);
+  }
+}
+
+test("same seed yields an identical draw sequence", () => {
+  const drawAll = () => [
+    strings().generate(),
+    integers().between(0, 999).generate(),
+    emails().domain("folio.app").generate(),
+    edgeCaseText().generate(),
+  ];
+  assert.deepEqual(withRng(7n, drawAll), withRng(7n, drawAll));
+});
+
+test("a different seed yields a different sequence", () => {
+  const drawAll = () => [strings().generate(), integers().generate()];
+  assert.notDeepEqual(withRng(1n, drawAll), withRng(2n, drawAll));
+});
+
+test("integers().between constrains the output range", () => {
+  withRng(42n, () => {
+    for (let i = 0; i < 200; i++) {
+      const value = integers().between(5, 9).generate();
+      assert.ok(Number.isInteger(value));
+      assert.ok(value >= 5 && value <= 9, `out of range: ${value}`);
+    }
+  });
+});
+
+test("strings().length(min, max).alpha() constrains length and charset", () => {
+  withRng(99n, () => {
+    for (let i = 0; i < 200; i++) {
+      const value = strings().length(3, 6).alpha().generate();
+      assert.ok(value.length >= 3 && value.length <= 6, `bad length: ${value}`);
+      assert.match(value, /^[A-Za-z]*$/);
+    }
+  });
+});
+
+test("emails().domain sets the host and edgeCaseText draws from the corpus", () => {
+  withRng(3n, () => {
+    const email = emails().domain("folio.app").generate();
+    assert.match(email, /^[A-Za-z]+@folio\.app$/);
+    assert.ok(INPUT_CORPUS.includes(edgeCaseText().generate()));
+  });
+});
+
+test("a builder is itself a Sampler<T>", () => {
+  withRng(11n, () => {
+    const sampler: Sampler<number> = integers().between(0, 9);
+    const value = sampler.generate();
+    assert.ok(value >= 0 && value <= 9);
+  });
+});
+
+test("outside a walk generators return a fixed deterministic default", () => {
+  setSamplerRng(null);
+  assert.equal(integers().between(10, 20).generate(), 10);
+  assert.equal(strings().length(4, 8).alpha().generate(), "aaaa");
+  assert.equal(emails().domain("folio.app").generate(), "[email protected]");
+  assert.equal(edgeCaseText().generate(), INPUT_CORPUS[0]);
+});