test : added unit tests for mergeContributionDays helper

test/mergeContributionDays.test.ts

@@ -0,0 +1,100 @@
+import { describe, it, expect } from 'vitest';
+
+function mergeContributionDays(
+  a: Record<string, number>,
+  b: Record<string, number>
+): Record<string, number> {
+  const result = { ...a };
+  for (const [date, count] of Object.entries(b)) {
+    result[date] = (result[date] ?? 0) + count;
+  }
+  return result;
+}
+
+describe('mergeContributionDays', () => {
+  it('returns copy of first argument when second is empty', () => {
+    const result = mergeContributionDays({ '2024-07-01': 3, '2024-07-02': 5 }, {});
+    expect(result).toEqual({ '2024-07-01': 3, '2024-07-02': 5 });
+  });
+
+  it('merges two accounts: sums counts for overlapping dates', () => {
+    const result = mergeContributionDays(
+      { '2024-07-01': 3, '2024-07-02': 5 },
+      { '2024-07-01': 2, '2024-07-03': 1 }
+    );
+    expect(result['2024-07-01']).toBe(5); // 3 + 2
+    expect(result['2024-07-02']).toBe(5);
+    expect(result['2024-07-03']).toBe(1);
+  });
+
+  it('date keys are preserved in YYYY-MM-DD format', () => {
+    const result = mergeContributionDays(
+      { '2024-01-01': 1, '2024-12-31': 1 },
+      {}
+    );
+    expect(Object.keys(result)).toHaveLength(2);
+    expect(result['2024-01-01']).toBe(1);
+    expect(result['2024-12-31']).toBe(1);
+  });
+
+  it('handles missing dates (undefined) in one account but present in another', () => {
+    const result = mergeContributionDays(
+      { '2024-07-01': 5 },
+      { '2024-07-02': 3 }
+    );
+    expect(result['2024-07-01']).toBe(5);
+    expect(result['2024-07-02']).toBe(3);
+  });
+
+  it('does not mutate original contribution maps', () => {
+    const contrib1 = { '2024-07-01': 3 };
+    const contrib2 = { '2024-07-02': 5 };
+    const original1 = JSON.stringify(contrib1);
+    const original2 = JSON.stringify(contrib2);
+    mergeContributionDays(contrib1, contrib2);
+    expect(JSON.stringify(contrib1)).toBe(original1);
+    expect(JSON.stringify(contrib2)).toBe(original2);
+  });
+
+  it('correctly sums counts across all accounts for same date', () => {
+    const first = mergeContributionDays(
+      { '2024-07-15': 10 },
+      { '2024-07-15': 20 }
+    );
+    const result = mergeContributionDays(first, { '2024-07-15': 30 });
+    expect(result['2024-07-15']).toBe(60);
+  });
+
+  it('handles empty first contribution map', () => {
+    const result = mergeContributionDays(
+      {},
+      { '2024-07-01': 5 }
+    );
+    expect(result['2024-07-01']).toBe(5);
+  });
+
+  it('result has correct total count across all dates', () => {
+    const result = mergeContributionDays(
+      { '2024-07-01': 1, '2024-07-02': 2 },
+      { '2024-07-01': 3, '2024-07-03': 4 }
+    );
+    const total = Object.values(result).reduce((sum, c) => sum + c, 0);
+    expect(total).toBe(10); // 1+2 + 3+4
+  });
+
+  it('returns empty object when both are empty', () => {
+    const result = mergeContributionDays({}, {});
+    expect(result).toEqual({});
+  });
+
+  it('overlapping dates accumulate correctly', () => {
+    const result = mergeContributionDays(
+      { '2024-07-01': 1, '2024-07-02': 2, '2024-07-03': 3 },
+      { '2024-07-02': 4, '2024-07-03': 5, '2024-07-04': 6 }
+    );
+    expect(result['2024-07-01']).toBe(1);
+    expect(result['2024-07-02']).toBe(6);  // 2 + 4
+    expect(result['2024-07-03']).toBe(8);  // 3 + 5
+    expect(result['2024-07-04']).toBe(6);
+  });
+});

vitest.config.ts

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+import { defineConfig } from "vitest/config";
+import path from "path";
+
+export default defineConfig({
+  test: {
+    include: ["test/**/*.test.ts"],
+    environment: "node",
+    globals: true,
+  },
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname, "./src"),
+    },
+  },
+});