test: add property and mutation coverage for core invariants

sdk/typescript/.gitignore

@@ -1,4 +1,6 @@
 /dist/
 /node_modules
+/reports/
+/.stryker-tmp/
 /private_release/dist/
 /*.tsbuildinfo

sdk/typescript/package.json

@@ -49,6 +49,7 @@
     "lint": "tsc --noEmit",
     "prepack": "node --run build",
     "test": "bun test --timeout 30000 ./tests-ts",
+    "test:mutation": "stryker run",
     "test:package": "node scripts/smoke-package.mjs",
     "types": "pnpm run generate:models:check && tsc --noEmit"
   },
@@ -68,9 +69,11 @@
     "smol-toml": "1.6.1"
   },
   "devDependencies": {
+    "@stryker-mutator/core": "9.6.1",
     "@types/bun": "1.3.13",
     "@types/node": "22.19.17",
     "@types/papaparse": "5.3.15",
+    "fast-check": "4.9.0",
     "json-schema-to-typescript": "15.0.4",
     "prettier": "3.2.5",
     "typescript": "5.7.3"

sdk/typescript/scripts/check-package.mjs

@@ -168,6 +168,7 @@ const distFiles = new Set(
     "config",
     "contract",
     "cost",
+    "cost-model",
     "errors",
     "index",
     "knowledge-base",

sdk/typescript/src/cost-model.ts

@@ -0,0 +1,122 @@
+export interface ScanCost {
+  model: string;
+  inputTokens: number;
+  cachedInputTokens: number;
+  cacheWriteInputTokens: number;
+  outputTokens: number;
+  estimatedUsd: number;
+}
+
+type ModelPricing = readonly [
+  input: number,
+  cachedInput: number,
+  cacheWriteInput: number,
+  output: number,
+];
+
+export interface ScanTokenUsage {
+  input_tokens: number;
+  cached_input_tokens: number;
+  cache_write_input_tokens: number;
+  output_tokens: number;
+  reasoning_output_tokens: number;
+  total_tokens: number;
+}
+
+const MODEL_PRICING_NANODOLLARS: Readonly<Record<string, ModelPricing>> = {
+  "gpt-5.6": [5_000, 500, 6_250, 30_000],
+  "gpt-5.6-sol": [5_000, 500, 6_250, 30_000],
+  "gpt-5.6-terra": [2_000, 200, 2_500, 12_000],
+  "gpt-5.6-luna": [200, 20, 250, 1_200],
+};
+
+export function tokenUsage(value: unknown): ScanTokenUsage | null {
+  if (!isRecord(value)) return null;
+  const input = value["input_tokens"];
+  const cached = value["cached_input_tokens"] ?? 0;
+  const canonicalCacheWrite = value["cache_write_input_tokens"];
+  const legacyCacheWrite = value["cache_write_tokens"];
+  const cacheWrite =
+    canonicalCacheWrite === 0 &&
+    isTokenCount(input) &&
+    isTokenCount(cached) &&
+    isTokenCount(legacyCacheWrite) &&
+    legacyCacheWrite > 0 &&
+    cached + legacyCacheWrite <= input
+      ? legacyCacheWrite
+      : canonicalCacheWrite ?? legacyCacheWrite ?? 0;
+  const output = value["output_tokens"];
+  const reasoning = value["reasoning_output_tokens"] ?? 0;
+  if (
+    !isTokenCount(input) ||
+    !isTokenCount(cached) ||
+    !isTokenCount(cacheWrite) ||
+    !isTokenCount(output) ||
+    !isTokenCount(reasoning) ||
+    cached + cacheWrite > input ||
+    reasoning > output
+  ) {
+    return null;
+  }
+  return {
+    input_tokens: input,
+    cached_input_tokens: cached,
+    cache_write_input_tokens: cacheWrite,
+    output_tokens: output,
+    reasoning_output_tokens: reasoning,
+    total_tokens: input + output,
+  };
+}
+
+export function estimateScanCost(
+  model: string | undefined,
+  usage: unknown,
+): ScanCost | null {
+  if (model === undefined) return null;
+  const pricingModel = model.startsWith("openai.")
+    ? model.slice("openai.".length)
+    : model;
+  const pricing = MODEL_PRICING_NANODOLLARS[pricingModel];
+  const normalized = tokenUsage(usage);
+  if (pricing === undefined || normalized === null) return null;
+  const [inputRate, cachedInputRate, cacheWriteInputRate, outputRate] = pricing;
+  const {
+    input_tokens: inputTokens,
+    cached_input_tokens: cachedInputTokens,
+    cache_write_input_tokens: cacheWriteInputTokens,
+    output_tokens: outputTokens,
+  } = normalized;
+
+  const nanodollars =
+    (inputTokens - cachedInputTokens - cacheWriteInputTokens) * inputRate +
+    cachedInputTokens * cachedInputRate +
+    cacheWriteInputTokens * cacheWriteInputRate +
+    outputTokens * outputRate;
+  if (!Number.isSafeInteger(nanodollars)) return null;
+
+  return {
+    model,
+    inputTokens,
+    cachedInputTokens,
+    cacheWriteInputTokens,
+    outputTokens,
+    estimatedUsd: nanodollars / 1_000_000_000,
+  };
+}
+
+export function formatUsd(value: number): string {
+  return new Intl.NumberFormat("en-US", {
+    style: "currency",
+    currency: "USD",
+    minimumFractionDigits: 2,
+    maximumFractionDigits: 9,
+  }).format(value);
+}
+
+function isTokenCount(value: unknown): value is number {
+  return typeof value === "number" && Number.isSafeInteger(value) && value >= 0;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null && !Array.isArray(value);
+}

sdk/typescript/src/cost.ts

@@ -1,3 +1,10 @@
+import {
+  estimateScanCost,
+  tokenUsage,
+  type ScanCost,
+  type ScanTokenUsage,
+} from "./cost-model.js";
+export { estimateScanCost, formatUsd, type ScanCost } from "./cost-model.js";
 import { open, readdir } from "node:fs/promises";
 import { join, relative, sep } from "node:path";
 import {
@@ -9,38 +16,13 @@ import {
   type ScanProgress,
 } from "./worker-progress.js";
 
-export interface ScanCost {
-  model: string;
-  inputTokens: number;
-  cachedInputTokens: number;
-  cacheWriteInputTokens: number;
-  outputTokens: number;
-  estimatedUsd: number;
-}
-
 export interface ScanSessionEvent {
   threadId: string;
   parentThreadId: string | null;
   worker?: number;
   event: Record<string, unknown>;
 }
 
-type ModelPricing = readonly [
-  input: number,
-  cachedInput: number,
-  cacheWriteInput: number,
-  output: number,
-];
-
-interface ScanTokenUsage {
-  input_tokens: number;
-  cached_input_tokens: number;
-  cache_write_input_tokens: number;
-  output_tokens: number;
-  reasoning_output_tokens: number;
-  total_tokens: number;
-}
-
 interface SessionReasoning {
   id: string;
   text: string;
@@ -90,13 +72,6 @@ interface ScanCostSnapshot {
   cost: ScanCost | null;
 }
 
-const MODEL_PRICING_NANODOLLARS: Readonly<Record<string, ModelPricing>> = {
-  "gpt-5.6": [5_000, 500, 6_250, 30_000],
-  "gpt-5.6-sol": [5_000, 500, 6_250, 30_000],
-  "gpt-5.6-terra": [2_000, 200, 2_500, 12_000],
-  "gpt-5.6-luna": [200, 20, 250, 1_200],
-};
-
 const COST_POLL_INTERVAL_MS = 100;
 const SESSION_READ_SIZE = 64 * 1_024;
 
@@ -781,44 +756,6 @@ function sessionContentText(
     .join("\n");
 }
 
-function tokenUsage(value: unknown): ScanTokenUsage | null {
-  if (!isRecord(value)) return null;
-  const input = value["input_tokens"];
-  const cached = value["cached_input_tokens"] ?? 0;
-  const canonicalCacheWrite = value["cache_write_input_tokens"];
-  const legacyCacheWrite = value["cache_write_tokens"];
-  const cacheWrite =
-    canonicalCacheWrite === 0 &&
-    isTokenCount(input) &&
-    isTokenCount(cached) &&
-    isTokenCount(legacyCacheWrite) &&
-    legacyCacheWrite > 0 &&
-    cached + legacyCacheWrite <= input
-      ? legacyCacheWrite
-      : canonicalCacheWrite ?? legacyCacheWrite ?? 0;
-  const output = value["output_tokens"];
-  const reasoning = value["reasoning_output_tokens"] ?? 0;
-  if (
-    !isTokenCount(input) ||
-    !isTokenCount(cached) ||
-    !isTokenCount(cacheWrite) ||
-    !isTokenCount(output) ||
-    !isTokenCount(reasoning) ||
-    cached + cacheWrite > input ||
-    reasoning > output
-  ) {
-    return null;
-  }
-  return {
-    input_tokens: input,
-    cached_input_tokens: cached,
-    cache_write_input_tokens: cacheWrite,
-    output_tokens: output,
-    reasoning_output_tokens: reasoning,
-    total_tokens: input + output,
-  };
-}
-
 function addTokenUsage(
   previous: ScanTokenUsage | null,
   next: ScanTokenUsage,
@@ -860,52 +797,3 @@ function isRecord(value: unknown): value is Record<string, unknown> {
 function isMissingFile(error: unknown): boolean {
   return isRecord(error) && error["code"] === "ENOENT";
 }
-
-export function estimateScanCost(
-  model: string | undefined,
-  usage: unknown,
-): ScanCost | null {
-  if (model === undefined) return null;
-  const pricingModel = model.startsWith("openai.")
-    ? model.slice("openai.".length)
-    : model;
-  const pricing = MODEL_PRICING_NANODOLLARS[pricingModel];
-  const normalized = tokenUsage(usage);
-  if (pricing === undefined || normalized === null) return null;
-  const [inputRate, cachedInputRate, cacheWriteInputRate, outputRate] = pricing;
-  const {
-    input_tokens: inputTokens,
-    cached_input_tokens: cachedInputTokens,
-    cache_write_input_tokens: cacheWriteInputTokens,
-    output_tokens: outputTokens,
-  } = normalized;
-
-  const nanodollars =
-    (inputTokens - cachedInputTokens - cacheWriteInputTokens) * inputRate +
-    cachedInputTokens * cachedInputRate +
-    cacheWriteInputTokens * cacheWriteInputRate +
-    outputTokens * outputRate;
-  if (!Number.isSafeInteger(nanodollars)) return null;
-
-  return {
-    model,
-    inputTokens,
-    cachedInputTokens,
-    cacheWriteInputTokens,
-    outputTokens,
-    estimatedUsd: nanodollars / 1_000_000_000,
-  };
-}
-
-export function formatUsd(value: number): string {
-  return new Intl.NumberFormat("en-US", {
-    style: "currency",
-    currency: "USD",
-    minimumFractionDigits: 2,
-    maximumFractionDigits: 9,
-  }).format(value);
-}
-
-function isTokenCount(value: unknown): value is number {
-  return typeof value === "number" && Number.isSafeInteger(value) && value >= 0;
-}

sdk/typescript/src/errors.ts

@@ -1,4 +1,4 @@
-import { formatUsd, type ScanCost } from "./cost.js";
+import { formatUsd, type ScanCost } from "./cost-model.js";
 
 /** Returns the original error message without altering its contents. */
 export function errorMessage(error: unknown): string {

sdk/typescript/stryker.config.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
+  "testRunner": "command",
+  "commandRunner": {
+    "command": "bun test --timeout 30000 ./tests-ts/cost-model.property.test.ts ./tests-ts/errors.test.ts ./tests-ts/errors.property.test.ts ./tests-ts/worker-progress.test.ts ./tests-ts/worker-progress.property.test.ts"
+  },
+  "mutate": ["src/cost-model.ts", "src/errors.ts", "src/worker-progress.ts"],
+  "coverageAnalysis": "off",
+  "reporters": ["clear-text", "progress", "json", "html"],
+  "concurrency": 2,
+  "thresholds": { "break": 0 }
+}