From eff2e618560e8805dab3ab94113b0dff8e72636b Mon Sep 17 00:00:00 2001
From: Jack Felke <jrinnfelke@gmail.com>
Date: Wed, 18 Mar 2026 14:47:54 -0700
Subject: [PATCH] test: add 31 unit tests for estimate_cost helpers

Export pure helper functions (estimateTokens, extractText, extractToolNames,
formatTokens, formatCost, formatDuration, analyzeSessionFile) and add
comprehensive tests covering:

- Token estimation (empty, short, long strings)
- Content extraction from string, block arrays, null/undefined
- Tool name extraction from content blocks
- Token/cost/duration formatting with edge cases
- Session file analysis: prompt counting, correction detection,
  tool call counting, preflight detection, timestamp tracking,
  empty files, and malformed JSON resilience

Brings test count from 43 to 74.
---
 src/tools/estimate-cost.ts        |  16 +-
 tests/tools/estimate-cost.test.ts | 273 ++++++++++++++++++++++++++++++
 2 files changed, 281 insertions(+), 8 deletions(-)
 create mode 100644 tests/tools/estimate-cost.test.ts

diff --git a/src/tools/estimate-cost.ts b/src/tools/estimate-cost.ts
index 327491a..f7477c7 100644
--- a/src/tools/estimate-cost.ts
+++ b/src/tools/estimate-cost.ts
@@ -31,11 +31,11 @@ const PREFLIGHT_TOOLS = new Set([
 
 // ── Helpers ─────────────────────────────────────────────────────────────────
 
-function estimateTokens(text: string): number {
+export function estimateTokens(text: string): number {
   return Math.ceil(text.length / 4);
 }
 
-function extractText(content: unknown): string {
+export function extractText(content: unknown): string {
   if (typeof content === "string") return content;
   if (Array.isArray(content)) {
     return content
@@ -46,25 +46,25 @@ function extractText(content: unknown): string {
   return "";
 }
 
-function extractToolNames(content: unknown): string[] {
+export function extractToolNames(content: unknown): string[] {
   if (!Array.isArray(content)) return [];
   return content
     .filter((b: any) => b.type === "tool_use" && b.name)
     .map((b: any) => b.name as string);
 }
 
-function formatTokens(n: number): string {
+export function formatTokens(n: number): string {
   if (n >= 1_000_000) return `${(n / 1_000_000).toFixed(1)}M`;
   if (n >= 1_000) return `${(n / 1_000).toFixed(1)}k`;
   return String(n);
 }
 
-function formatCost(dollars: number): string {
+export function formatCost(dollars: number): string {
   if (dollars < 0.01) return `<$0.01`;
   return `$${dollars.toFixed(2)}`;
 }
 
-function formatDuration(ms: number): string {
+export function formatDuration(ms: number): string {
   const mins = Math.floor(ms / 60_000);
   if (mins < 60) return `${mins}m`;
   const hours = Math.floor(mins / 60);
@@ -72,7 +72,7 @@ function formatDuration(ms: number): string {
   return `${hours}h ${rem}m`;
 }
 
-interface SessionAnalysis {
+export interface SessionAnalysis {
   inputTokens: number;
   outputTokens: number;
   promptCount: number;
@@ -85,7 +85,7 @@ interface SessionAnalysis {
   lastTimestamp: string | null;
 }
 
-function analyzeSessionFile(filePath: string): SessionAnalysis {
+export function analyzeSessionFile(filePath: string): SessionAnalysis {
   const content = readFileSync(filePath, "utf-8");
   const lines = content.trim().split("\n").filter(Boolean);
 
diff --git a/tests/tools/estimate-cost.test.ts b/tests/tools/estimate-cost.test.ts
new file mode 100644
index 0000000..8ee248f
--- /dev/null
+++ b/tests/tools/estimate-cost.test.ts
@@ -0,0 +1,273 @@
+import { describe, it, expect } from "vitest";
+import { writeFileSync, mkdirSync, rmSync } from "fs";
+import { join } from "path";
+import { tmpdir } from "os";
+import {
+  estimateTokens,
+  extractText,
+  extractToolNames,
+  formatTokens,
+  formatCost,
+  formatDuration,
+  analyzeSessionFile,
+} from "../../src/tools/estimate-cost.js";
+
+// ── estimateTokens ──────────────────────────────────────────────────────────
+
+describe("estimateTokens", () => {
+  it("returns ~1 token per 4 chars", () => {
+    expect(estimateTokens("abcd")).toBe(1);
+    expect(estimateTokens("abcde")).toBe(2); // ceil(5/4)
+  });
+
+  it("handles empty string", () => {
+    expect(estimateTokens("")).toBe(0);
+  });
+
+  it("handles long text", () => {
+    const text = "x".repeat(1000);
+    expect(estimateTokens(text)).toBe(250);
+  });
+});
+
+// ── extractText ─────────────────────────────────────────────────────────────
+
+describe("extractText", () => {
+  it("returns string content as-is", () => {
+    expect(extractText("hello world")).toBe("hello world");
+  });
+
+  it("extracts text from content block array", () => {
+    const blocks = [
+      { type: "text", text: "first" },
+      { type: "text", text: "second" },
+    ];
+    expect(extractText(blocks)).toBe("first\nsecond");
+  });
+
+  it("skips non-text blocks", () => {
+    const blocks = [
+      { type: "text", text: "keep" },
+      { type: "tool_use", name: "read", input: {} },
+      { type: "text", text: "also keep" },
+    ];
+    expect(extractText(blocks)).toBe("keep\nalso keep");
+  });
+
+  it("returns empty string for null/undefined", () => {
+    expect(extractText(null)).toBe("");
+    expect(extractText(undefined)).toBe("");
+  });
+
+  it("returns empty string for number", () => {
+    expect(extractText(42)).toBe("");
+  });
+
+  it("returns empty string for object", () => {
+    expect(extractText({ foo: "bar" })).toBe("");
+  });
+
+  it("handles empty array", () => {
+    expect(extractText([])).toBe("");
+  });
+});
+
+// ── extractToolNames ────────────────────────────────────────────────────────
+
+describe("extractToolNames", () => {
+  it("extracts tool names from content blocks", () => {
+    const blocks = [
+      { type: "text", text: "I'll read the file" },
+      { type: "tool_use", name: "Read", input: { path: "foo.ts" } },
+      { type: "tool_use", name: "Edit", input: { path: "bar.ts" } },
+    ];
+    expect(extractToolNames(blocks)).toEqual(["Read", "Edit"]);
+  });
+
+  it("returns empty for non-array", () => {
+    expect(extractToolNames("string")).toEqual([]);
+    expect(extractToolNames(null)).toEqual([]);
+    expect(extractToolNames(42)).toEqual([]);
+  });
+
+  it("skips blocks without name", () => {
+    const blocks = [
+      { type: "tool_use" },
+      { type: "tool_use", name: "Read", input: {} },
+    ];
+    expect(extractToolNames(blocks)).toEqual(["Read"]);
+  });
+
+  it("handles empty array", () => {
+    expect(extractToolNames([])).toEqual([]);
+  });
+});
+
+// ── formatTokens ────────────────────────────────────────────────────────────
+
+describe("formatTokens", () => {
+  it("formats small numbers as-is", () => {
+    expect(formatTokens(500)).toBe("500");
+  });
+
+  it("formats thousands as k", () => {
+    expect(formatTokens(1000)).toBe("1.0k");
+    expect(formatTokens(15_500)).toBe("15.5k");
+  });
+
+  it("formats millions as M", () => {
+    expect(formatTokens(1_000_000)).toBe("1.0M");
+    expect(formatTokens(2_500_000)).toBe("2.5M");
+  });
+
+  it("formats zero", () => {
+    expect(formatTokens(0)).toBe("0");
+  });
+});
+
+// ── formatCost ──────────────────────────────────────────────────────────────
+
+describe("formatCost", () => {
+  it("formats normal costs", () => {
+    expect(formatCost(1.5)).toBe("$1.50");
+    expect(formatCost(0.05)).toBe("$0.05");
+  });
+
+  it("formats very small costs", () => {
+    expect(formatCost(0.001)).toBe("<$0.01");
+    expect(formatCost(0.009)).toBe("<$0.01");
+  });
+
+  it("formats zero", () => {
+    expect(formatCost(0)).toBe("<$0.01");
+  });
+});
+
+// ── formatDuration ──────────────────────────────────────────────────────────
+
+describe("formatDuration", () => {
+  it("formats minutes", () => {
+    expect(formatDuration(5 * 60_000)).toBe("5m");
+    expect(formatDuration(45 * 60_000)).toBe("45m");
+  });
+
+  it("formats hours and minutes", () => {
+    expect(formatDuration(90 * 60_000)).toBe("1h 30m");
+    expect(formatDuration(125 * 60_000)).toBe("2h 5m");
+  });
+
+  it("formats zero", () => {
+    expect(formatDuration(0)).toBe("0m");
+  });
+});
+
+// ── analyzeSessionFile ──────────────────────────────────────────────────────
+
+describe("analyzeSessionFile", () => {
+  const tmpDir = join(tmpdir(), "preflight-test-estimate-cost");
+
+  function writeSession(name: string, lines: object[]): string {
+    mkdirSync(tmpDir, { recursive: true });
+    const path = join(tmpDir, name);
+    writeFileSync(path, lines.map((l) => JSON.stringify(l)).join("\n"));
+    return path;
+  }
+
+  afterAll(() => {
+    try { rmSync(tmpDir, { recursive: true, force: true }); } catch {}
+  });
+
+  it("counts user prompts and assistant responses", () => {
+    const path = writeSession("basic.jsonl", [
+      { type: "user", timestamp: "2025-01-01T00:00:00Z", message: { content: "hello world" } },
+      { type: "assistant", timestamp: "2025-01-01T00:01:00Z", message: { content: "hi there, how can I help?" } },
+      { type: "user", timestamp: "2025-01-01T00:02:00Z", message: { content: "do something" } },
+      { type: "assistant", timestamp: "2025-01-01T00:03:00Z", message: { content: "done!" } },
+    ]);
+    const result = analyzeSessionFile(path);
+    expect(result.promptCount).toBe(2);
+    expect(result.inputTokens).toBeGreaterThan(0);
+    expect(result.outputTokens).toBeGreaterThan(0);
+  });
+
+  it("detects corrections", () => {
+    const path = writeSession("corrections.jsonl", [
+      { type: "user", timestamp: "2025-01-01T00:00:00Z", message: { content: "add a button" } },
+      { type: "assistant", timestamp: "2025-01-01T00:01:00Z", message: { content: "I added a red button to the header component." } },
+      { type: "user", timestamp: "2025-01-01T00:02:00Z", message: { content: "no, wrong file. I meant the footer." } },
+    ]);
+    const result = analyzeSessionFile(path);
+    expect(result.corrections).toBe(1);
+    expect(result.wastedOutputTokens).toBeGreaterThan(0);
+  });
+
+  it("counts tool calls", () => {
+    const path = writeSession("tools.jsonl", [
+      { type: "user", timestamp: "2025-01-01T00:00:00Z", message: { content: "read the file" } },
+      {
+        type: "assistant",
+        timestamp: "2025-01-01T00:01:00Z",
+        message: {
+          content: [
+            { type: "text", text: "I'll read the file." },
+            { type: "tool_use", name: "Read", id: "t1", input: { path: "foo.ts" } },
+          ],
+        },
+      },
+      { type: "tool_result", tool_use_id: "t1", content: "file contents here" },
+    ]);
+    const result = analyzeSessionFile(path);
+    expect(result.toolCallCount).toBe(1);
+  });
+
+  it("detects preflight tool calls", () => {
+    const path = writeSession("preflight.jsonl", [
+      { type: "user", timestamp: "2025-01-01T00:00:00Z", message: { content: "check my code" } },
+      {
+        type: "assistant",
+        timestamp: "2025-01-01T00:01:00Z",
+        message: {
+          content: [
+            { type: "text", text: "Running preflight check." },
+            { type: "tool_use", name: "preflight_check", id: "t1", input: { task: "review code" } },
+          ],
+        },
+      },
+    ]);
+    const result = analyzeSessionFile(path);
+    expect(result.preflightCalls).toBe(1);
+    expect(result.preflightTokens).toBeGreaterThan(0);
+  });
+
+  it("tracks timestamps", () => {
+    const path = writeSession("timestamps.jsonl", [
+      { type: "user", timestamp: "2025-01-01T10:00:00Z", message: { content: "start" } },
+      { type: "assistant", timestamp: "2025-01-01T10:30:00Z", message: { content: "end" } },
+    ]);
+    const result = analyzeSessionFile(path);
+    expect(result.firstTimestamp).toBe("2025-01-01T10:00:00Z");
+    expect(result.lastTimestamp).toBe("2025-01-01T10:30:00Z");
+  });
+
+  it("handles empty file", () => {
+    const path = writeSession("empty.jsonl", []);
+    writeFileSync(path, "");
+    const result = analyzeSessionFile(path);
+    expect(result.promptCount).toBe(0);
+    expect(result.inputTokens).toBe(0);
+    expect(result.outputTokens).toBe(0);
+  });
+
+  it("skips malformed JSON lines", () => {
+    const path = join(tmpDir, "malformed.jsonl");
+    mkdirSync(tmpDir, { recursive: true });
+    writeFileSync(path, [
+      '{"type":"user","timestamp":"2025-01-01T00:00:00Z","message":{"content":"hello"}}',
+      "not valid json",
+      '{"type":"assistant","timestamp":"2025-01-01T00:01:00Z","message":{"content":"hi"}}',
+    ].join("\n"));
+    const result = analyzeSessionFile(path);
+    expect(result.promptCount).toBe(1);
+    expect(result.outputTokens).toBeGreaterThan(0);
+  });
+});