feat: add tests and assert coverage (#71)

### Explanation

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### Attestations

- [ ] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [ ] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

- [ ] I have run the linter and resolved any errors.
- [ ] My pull request uses an appropriate title, matching the conventional commit standards.
- [ ] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
- [ ] Code coverage remains at or above the configured threshold.

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Co-authored-by: Hikari <hikari@nhcarrigan.com>
Reviewed-on: #71
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/lib/stores/stats.test.ts

@@ -0,0 +1,346 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { get } from "svelte/store";
+import { stats, formattedStats, resetSessionStats } from "./stats";
+import type { UsageStats } from "./stats";
+
+// Mock Tauri APIs
+vi.mock("@tauri-apps/api/event", () => ({
+  listen: vi.fn(),
+}));
+
+vi.mock("@tauri-apps/api/core", () => ({
+  invoke: vi.fn(),
+}));
+
+describe("stats store", () => {
+  beforeEach(() => {
+    // Reset stats to default before each test
+    stats.set({
+      total_input_tokens: 0,
+      total_output_tokens: 0,
+      total_cost_usd: 0,
+      session_input_tokens: 0,
+      session_output_tokens: 0,
+      session_cost_usd: 0,
+      model: null,
+      messages_exchanged: 0,
+      session_messages_exchanged: 0,
+      code_blocks_generated: 0,
+      session_code_blocks_generated: 0,
+      files_edited: 0,
+      session_files_edited: 0,
+      files_created: 0,
+      session_files_created: 0,
+      tools_usage: {},
+      session_tools_usage: {},
+      session_duration_seconds: 0,
+    });
+  });
+
+  describe("stats writable store", () => {
+    it("has correct default values", () => {
+      const currentStats = get(stats);
+      expect(currentStats.total_input_tokens).toBe(0);
+      expect(currentStats.total_output_tokens).toBe(0);
+      expect(currentStats.total_cost_usd).toBe(0);
+      expect(currentStats.model).toBeNull();
+    });
+
+    it("can be updated with set", () => {
+      const newStats: UsageStats = {
+        total_input_tokens: 1000,
+        total_output_tokens: 2000,
+        total_cost_usd: 0.05,
+        session_input_tokens: 500,
+        session_output_tokens: 1000,
+        session_cost_usd: 0.025,
+        model: "claude-sonnet-4",
+        messages_exchanged: 10,
+        session_messages_exchanged: 5,
+        code_blocks_generated: 3,
+        session_code_blocks_generated: 2,
+        files_edited: 5,
+        session_files_edited: 2,
+        files_created: 1,
+        session_files_created: 1,
+        tools_usage: { Read: 5, Edit: 3 },
+        session_tools_usage: { Read: 2, Edit: 1 },
+        session_duration_seconds: 300,
+      };
+
+      stats.set(newStats);
+      const currentStats = get(stats);
+
+      expect(currentStats.total_input_tokens).toBe(1000);
+      expect(currentStats.total_output_tokens).toBe(2000);
+      expect(currentStats.model).toBe("claude-sonnet-4");
+      expect(currentStats.tools_usage).toEqual({ Read: 5, Edit: 3 });
+    });
+
+    it("can be updated with update function", () => {
+      stats.update((current) => ({
+        ...current,
+        total_input_tokens: 500,
+        session_messages_exchanged: 3,
+      }));
+
+      const currentStats = get(stats);
+      expect(currentStats.total_input_tokens).toBe(500);
+      expect(currentStats.session_messages_exchanged).toBe(3);
+    });
+  });
+
+  describe("resetSessionStats", () => {
+    it("resets all session fields to zero", () => {
+      // First set some values
+      stats.set({
+        total_input_tokens: 1000,
+        total_output_tokens: 2000,
+        total_cost_usd: 0.05,
+        session_input_tokens: 500,
+        session_output_tokens: 1000,
+        session_cost_usd: 0.025,
+        model: "claude-sonnet-4",
+        messages_exchanged: 10,
+        session_messages_exchanged: 5,
+        code_blocks_generated: 3,
+        session_code_blocks_generated: 2,
+        files_edited: 5,
+        session_files_edited: 2,
+        files_created: 1,
+        session_files_created: 1,
+        tools_usage: { Read: 5, Edit: 3 },
+        session_tools_usage: { Read: 2, Edit: 1 },
+        session_duration_seconds: 300,
+      });
+
+      // Reset session stats
+      resetSessionStats();
+
+      const currentStats = get(stats);
+
+      // Total stats should be preserved
+      expect(currentStats.total_input_tokens).toBe(1000);
+      expect(currentStats.total_output_tokens).toBe(2000);
+      expect(currentStats.total_cost_usd).toBe(0.05);
+      expect(currentStats.messages_exchanged).toBe(10);
+      expect(currentStats.code_blocks_generated).toBe(3);
+      expect(currentStats.files_edited).toBe(5);
+      expect(currentStats.files_created).toBe(1);
+      expect(currentStats.tools_usage).toEqual({ Read: 5, Edit: 3 });
+      expect(currentStats.model).toBe("claude-sonnet-4");
+
+      // Session stats should be reset
+      expect(currentStats.session_input_tokens).toBe(0);
+      expect(currentStats.session_output_tokens).toBe(0);
+      expect(currentStats.session_cost_usd).toBe(0);
+      expect(currentStats.session_messages_exchanged).toBe(0);
+      expect(currentStats.session_code_blocks_generated).toBe(0);
+      expect(currentStats.session_files_edited).toBe(0);
+      expect(currentStats.session_files_created).toBe(0);
+      expect(currentStats.session_tools_usage).toEqual({});
+      expect(currentStats.session_duration_seconds).toBe(0);
+    });
+  });
+
+  describe("formattedStats derived store", () => {
+    it("formats token numbers with locale string", () => {
+      stats.update((current) => ({
+        ...current,
+        total_input_tokens: 1234567,
+        total_output_tokens: 7654321,
+        session_input_tokens: 12345,
+        session_output_tokens: 54321,
+      }));
+
+      const formatted = get(formattedStats);
+
+      expect(formatted.totalTokens).toBe("8,888,888");
+      expect(formatted.totalInputTokens).toBe("1,234,567");
+      expect(formatted.totalOutputTokens).toBe("7,654,321");
+      expect(formatted.sessionTokens).toBe("66,666");
+      expect(formatted.sessionInputTokens).toBe("12,345");
+      expect(formatted.sessionOutputTokens).toBe("54,321");
+    });
+
+    it("formats cost with 4 decimal places", () => {
+      stats.update((current) => ({
+        ...current,
+        total_cost_usd: 1.23456,
+        session_cost_usd: 0.00123,
+      }));
+
+      const formatted = get(formattedStats);
+
+      expect(formatted.totalCost).toBe("$1.2346");
+      expect(formatted.sessionCost).toBe("$0.0012");
+    });
+
+    it("formats duration seconds only", () => {
+      stats.update((current) => ({
+        ...current,
+        session_duration_seconds: 45,
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.sessionDuration).toBe("45s");
+    });
+
+    it("formats duration minutes and seconds", () => {
+      stats.update((current) => ({
+        ...current,
+        session_duration_seconds: 125, // 2m 5s
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.sessionDuration).toBe("2m 5s");
+    });
+
+    it("formats duration hours, minutes, and seconds", () => {
+      stats.update((current) => ({
+        ...current,
+        session_duration_seconds: 3725, // 1h 2m 5s
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.sessionDuration).toBe("1h 2m 5s");
+    });
+
+    it("formats duration with zero seconds", () => {
+      stats.update((current) => ({
+        ...current,
+        session_duration_seconds: 3600, // exactly 1h
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.sessionDuration).toBe("1h 0m 0s");
+    });
+
+    it("shows model name when available", () => {
+      stats.update((current) => ({
+        ...current,
+        model: "claude-opus-4-5",
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.model).toBe("claude-opus-4-5");
+    });
+
+    it("shows placeholder when model is null", () => {
+      stats.update((current) => ({
+        ...current,
+        model: null,
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.model).toBe("No model selected");
+    });
+
+    it("formats message counts", () => {
+      stats.update((current) => ({
+        ...current,
+        messages_exchanged: 100,
+        session_messages_exchanged: 10,
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.messagesTotal).toBe("100");
+      expect(formatted.messagesSession).toBe("10");
+    });
+
+    it("formats code block counts", () => {
+      stats.update((current) => ({
+        ...current,
+        code_blocks_generated: 50,
+        session_code_blocks_generated: 5,
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.codeBlocksTotal).toBe("50");
+      expect(formatted.codeBlocksSession).toBe("5");
+    });
+
+    it("formats file counts", () => {
+      stats.update((current) => ({
+        ...current,
+        files_edited: 25,
+        session_files_edited: 3,
+        files_created: 10,
+        session_files_created: 2,
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.filesEditedTotal).toBe("25");
+      expect(formatted.filesEditedSession).toBe("3");
+      expect(formatted.filesCreatedTotal).toBe("10");
+      expect(formatted.filesCreatedSession).toBe("2");
+    });
+
+    it("exposes tools usage directly", () => {
+      const toolsUsage = { Read: 10, Edit: 5, Write: 3 };
+      const sessionToolsUsage = { Read: 2, Edit: 1 };
+
+      stats.update((current) => ({
+        ...current,
+        tools_usage: toolsUsage,
+        session_tools_usage: sessionToolsUsage,
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.toolsUsage).toEqual(toolsUsage);
+      expect(formatted.sessionToolsUsage).toEqual(sessionToolsUsage);
+    });
+
+    it("handles zero values correctly", () => {
+      const formatted = get(formattedStats);
+
+      expect(formatted.totalTokens).toBe("0");
+      expect(formatted.totalCost).toBe("$0.0000");
+      expect(formatted.sessionDuration).toBe("0s");
+      expect(formatted.messagesTotal).toBe("0");
+    });
+
+    it("handles large numbers with proper formatting", () => {
+      stats.update((current) => ({
+        ...current,
+        total_input_tokens: 1000000000, // 1 billion
+        messages_exchanged: 999999,
+      }));
+
+      const formatted = get(formattedStats);
+      expect(formatted.totalInputTokens).toBe("1,000,000,000");
+      expect(formatted.messagesTotal).toBe("999,999");
+    });
+  });
+
+  describe("UsageStats interface", () => {
+    it("supports all expected fields", () => {
+      const fullStats: UsageStats = {
+        total_input_tokens: 100,
+        total_output_tokens: 200,
+        total_cost_usd: 0.01,
+        session_input_tokens: 50,
+        session_output_tokens: 100,
+        session_cost_usd: 0.005,
+        model: "test-model",
+        messages_exchanged: 5,
+        session_messages_exchanged: 2,
+        code_blocks_generated: 3,
+        session_code_blocks_generated: 1,
+        files_edited: 2,
+        session_files_edited: 1,
+        files_created: 1,
+        session_files_created: 0,
+        tools_usage: { Read: 3 },
+        session_tools_usage: { Read: 1 },
+        session_duration_seconds: 60,
+      };
+
+      stats.set(fullStats);
+      const currentStats = get(stats);
+
+      // Verify all fields are present and correct
+      expect(currentStats).toEqual(fullStats);
+    });
+  });
+});