feat: Display initial token usage metrics in /stats (#879)

packages/cli/src/ui/contexts/SessionContext.test.tsx

@@ -4,26 +4,181 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import { type MutableRefObject } from 'react';
 import { render } from 'ink-testing-library';
-import { Text } from 'ink';
-import { SessionProvider, useSession } from './SessionContext.js';
-import { describe, it, expect } from 'vitest';
+import { act } from 'react-dom/test-utils';
+import { SessionStatsProvider, useSessionStats } from './SessionContext.js';
+import { describe, it, expect, vi } from 'vitest';
+import { GenerateContentResponseUsageMetadata } from '@google/genai';
 
-const TestComponent = () => {
-  const { startTime } = useSession();
-  return <Text>{startTime.toISOString()}</Text>;
+// Mock data that simulates what the Gemini API would return.
+const mockMetadata1: GenerateContentResponseUsageMetadata = {
+  promptTokenCount: 100,
+  candidatesTokenCount: 200,
+  totalTokenCount: 300,
+  cachedContentTokenCount: 50,
+  toolUsePromptTokenCount: 10,
+  thoughtsTokenCount: 20,
 };
 
-describe('SessionContext', () => {
-  it('should provide a start time', () => {
-    const { lastFrame } = render(
-      <SessionProvider>
-        <TestComponent />
-      </SessionProvider>,
+const mockMetadata2: GenerateContentResponseUsageMetadata = {
+  promptTokenCount: 10,
+  candidatesTokenCount: 20,
+  totalTokenCount: 30,
+  cachedContentTokenCount: 5,
+  toolUsePromptTokenCount: 1,
+  thoughtsTokenCount: 2,
+};
+
+/**
+ * A test harness component that uses the hook and exposes the context value
+ * via a mutable ref. This allows us to interact with the context's functions
+ * and assert against its state directly in our tests.
+ */
+const TestHarness = ({
+  contextRef,
+}: {
+  contextRef: MutableRefObject<ReturnType<typeof useSessionStats> | undefined>;
+}) => {
+  contextRef.current = useSessionStats();
+  return null;
+};
+
+describe('SessionStatsContext', () => {
+  it('should provide the correct initial state', () => {
+    const contextRef: MutableRefObject<
+      ReturnType<typeof useSessionStats> | undefined
+    > = { current: undefined };
+
+    render(
+      <SessionStatsProvider>
+        <TestHarness contextRef={contextRef} />
+      </SessionStatsProvider>,
     );
 
-    const frameText = lastFrame();
-    // Check if the output is a valid ISO string, which confirms it's a Date object.
-    expect(new Date(frameText!).toString()).not.toBe('Invalid Date');
+    const stats = contextRef.current?.stats;
+
+    expect(stats?.sessionStartTime).toBeInstanceOf(Date);
+    expect(stats?.lastTurn).toBeNull();
+    expect(stats?.cumulative.turnCount).toBe(0);
+    expect(stats?.cumulative.totalTokenCount).toBe(0);
+    expect(stats?.cumulative.promptTokenCount).toBe(0);
+  });
+
+  it('should increment turnCount when startNewTurn is called', () => {
+    const contextRef: MutableRefObject<
+      ReturnType<typeof useSessionStats> | undefined
+    > = { current: undefined };
+
+    render(
+      <SessionStatsProvider>
+        <TestHarness contextRef={contextRef} />
+      </SessionStatsProvider>,
+    );
+
+    act(() => {
+      contextRef.current?.startNewTurn();
+    });
+
+    const stats = contextRef.current?.stats;
+    expect(stats?.cumulative.turnCount).toBe(1);
+    // Ensure token counts are unaffected
+    expect(stats?.cumulative.totalTokenCount).toBe(0);
+  });
+
+  it('should aggregate token usage correctly when addUsage is called', () => {
+    const contextRef: MutableRefObject<
+      ReturnType<typeof useSessionStats> | undefined
+    > = { current: undefined };
+
+    render(
+      <SessionStatsProvider>
+        <TestHarness contextRef={contextRef} />
+      </SessionStatsProvider>,
+    );
+
+    act(() => {
+      contextRef.current?.addUsage(mockMetadata1);
+    });
+
+    const stats = contextRef.current?.stats;
+
+    // Check that token counts are updated
+    expect(stats?.cumulative.totalTokenCount).toBe(
+      mockMetadata1.totalTokenCount ?? 0,
+    );
+    expect(stats?.cumulative.promptTokenCount).toBe(
+      mockMetadata1.promptTokenCount ?? 0,
+    );
+
+    // Check that turn count is NOT incremented
+    expect(stats?.cumulative.turnCount).toBe(0);
+
+    // Check that lastTurn is updated
+    expect(stats?.lastTurn?.metadata).toEqual(mockMetadata1);
+  });
+
+  it('should correctly track a full logical turn with multiple API calls', () => {
+    const contextRef: MutableRefObject<
+      ReturnType<typeof useSessionStats> | undefined
+    > = { current: undefined };
+
+    render(
+      <SessionStatsProvider>
+        <TestHarness contextRef={contextRef} />
+      </SessionStatsProvider>,
+    );
+
+    // 1. User starts a new turn
+    act(() => {
+      contextRef.current?.startNewTurn();
+    });
+
+    // 2. First API call (e.g., prompt with a tool request)
+    act(() => {
+      contextRef.current?.addUsage(mockMetadata1);
+    });
+
+    // 3. Second API call (e.g., sending tool response back)
+    act(() => {
+      contextRef.current?.addUsage(mockMetadata2);
+    });
+
+    const stats = contextRef.current?.stats;
+
+    // Turn count should only be 1
+    expect(stats?.cumulative.turnCount).toBe(1);
+
+    // These fields should be the SUM of both calls
+    expect(stats?.cumulative.totalTokenCount).toBe(330); // 300 + 30
+    expect(stats?.cumulative.candidatesTokenCount).toBe(220); // 200 + 20
+    expect(stats?.cumulative.thoughtsTokenCount).toBe(22); // 20 + 2
+
+    // These fields should ONLY be from the FIRST call, because isNewTurnForAggregation was true
+    expect(stats?.cumulative.promptTokenCount).toBe(100);
+    expect(stats?.cumulative.cachedContentTokenCount).toBe(50);
+    expect(stats?.cumulative.toolUsePromptTokenCount).toBe(10);
+
+    // Last turn should hold the metadata from the most recent call
+    expect(stats?.lastTurn?.metadata).toEqual(mockMetadata2);
+  });
+
+  it('should throw an error when useSessionStats is used outside of a provider', () => {
+    // Suppress the expected console error during this test.
+    const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+
+    const contextRef = { current: undefined };
+
+    // We expect rendering to fail, which React will catch and log as an error.
+    render(<TestHarness contextRef={contextRef} />);
+
+    // Assert that the first argument of the first call to console.error
+    // contains the expected message. This is more robust than checking
+    // the exact arguments, which can be affected by React/JSDOM internals.
+    expect(errorSpy.mock.calls[0][0]).toContain(
+      'useSessionStats must be used within a SessionStatsProvider',
+    );
+
+    errorSpy.mockRestore();
   });
 });