Fix short numbers rounding up instead of truncating (#37899) (#38114)

app/javascript/mastodon/components/__tests__/short_number-test.tsx

@@ -0,0 +1,80 @@
+import { IntlProvider } from 'react-intl';
+
+import { render, screen } from '@testing-library/react';
+
+import { ShortNumber } from '../short_number';
+
+function renderShortNumber(value: number) {
+  return render(
+    <IntlProvider locale='en'>
+      <ShortNumber value={value} />
+    </IntlProvider>,
+  );
+}
+
+describe('ShortNumber Component', () => {
+  it('does not abbreviate numbers under 1000', () => {
+    renderShortNumber(999);
+    expect(screen.getByText('999')).toBeDefined();
+  });
+
+  it('formats thousands correctly for 1000', () => {
+    renderShortNumber(1000);
+    expect(screen.getByText('1K')).toBeDefined();
+  });
+
+  it('truncates decimals for 1051', () => {
+    renderShortNumber(1051);
+    expect(screen.getByText('1K')).toBeDefined();
+  });
+
+  it('truncates decimals for 2999', () => {
+    renderShortNumber(2999);
+    expect(screen.getByText('2.9K')).toBeDefined();
+  });
+
+  it('truncates decimals for 9999', () => {
+    renderShortNumber(9999);
+    expect(screen.getByText('9.9K')).toBeDefined();
+  });
+
+  it('truncates decimals for 10501', () => {
+    renderShortNumber(10501);
+    expect(screen.getByText('10K')).toBeDefined();
+  });
+
+  it('truncates decimals for 11000', () => {
+    renderShortNumber(11000);
+    expect(screen.getByText('11K')).toBeDefined();
+  });
+
+  it('truncates decimals for 99999', () => {
+    renderShortNumber(99999);
+    expect(screen.getByText('99K')).toBeDefined();
+  });
+
+  it('truncates decimals for 100501', () => {
+    renderShortNumber(100501);
+    expect(screen.getByText('100K')).toBeDefined();
+  });
+
+  it('truncates decimals for 101000', () => {
+    renderShortNumber(101000);
+    expect(screen.getByText('101K')).toBeDefined();
+  });
+
+  it('truncates decimals for 999999', () => {
+    renderShortNumber(999999);
+    expect(screen.getByText('999K')).toBeDefined();
+  });
+
+  it('truncates decimals for 2999999', () => {
+    renderShortNumber(2999999);
+    expect(screen.getByText('2.9M')).toBeDefined();
+  });
+
+  it('truncates decimals for 9999999', () => {
+    renderShortNumber(9999999);
+    expect(screen.getByText('9.9M')).toBeDefined();
+  });
+});

app/javascript/mastodon/components/short_number.tsx

@@ -51,6 +51,7 @@ const ShortNumberCounter: React.FC<ShortNumberCounterProps> = ({ value }) => {
     <FormattedNumber
       value={rawNumber ?? 0}
       maximumFractionDigits={maxFractionDigits}
+      roundingMode='trunc'
     />
   );