diff --git a/src/entities/Font/lib/dualFontLayout/DualFontLayout/DualFontLayout.test.ts b/src/entities/Font/lib/dualFontLayout/DualFontLayout/DualFontLayout.test.ts
new file mode 100644
index 0000000..f3bc49f
--- /dev/null
+++ b/src/entities/Font/lib/dualFontLayout/DualFontLayout/DualFontLayout.test.ts
@@ -0,0 +1,95 @@
+// @vitest-environment jsdom
+import { installCanvasMock } from '$shared/lib/helpers/__mocks__/canvas';
+import { clearCache } from '@chenglou/pretext';
+import {
+    beforeEach,
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import { DualFontLayout } from './DualFontLayout';
+
+// FontA: 10px per character. FontB: 15px per character.
+// The mock dispatches on whether the font string contains 'FontA' or 'FontB'.
+const FONT_A_WIDTH = 10;
+const FONT_B_WIDTH = 15;
+
+function fontWidthFactory(font: string, text: string): number {
+    const perChar = font.includes('FontA') ? FONT_A_WIDTH : FONT_B_WIDTH;
+    return text.length * perChar;
+}
+
+describe('DualFontLayout', () => {
+    let layout: DualFontLayout;
+
+    beforeEach(() => {
+        installCanvasMock(fontWidthFactory);
+        clearCache();
+        layout = new DualFontLayout();
+    });
+
+    it('returns empty result for empty string', () => {
+        const result = layout.layout('', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        expect(result.lines).toHaveLength(0);
+        expect(result.totalHeight).toBe(0);
+    });
+
+    it('uses worst-case width across both fonts to determine line breaks', () => {
+        // 'AB CD' — two 2-char words separated by a space.
+        // FontA: 'AB'=20px, 'CD'=20px. Both fit in 25px? No: 'AB CD' = 50px total.
+        // FontB: 'AB'=30px, 'CD'=30px. Width 35px forces wrap after 'AB '.
+        // Unified must use FontB widths — so it must wrap at the same place FontB wraps.
+        const result = layout.layout('AB CD', '400 16px "FontA"', '400 16px "FontB"', 35, 20);
+        expect(result.lines.length).toBeGreaterThan(1);
+        // First line text must not include both words.
+        expect(result.lines[0].text).not.toContain('CD');
+    });
+
+    it('provides xA and xB offsets for both fonts on a single line', () => {
+        // 'ABC' fits in 500px for both fonts.
+        // FontA: A@0(w=10), B@10(w=10), C@20(w=10)
+        // FontB: A@0(w=15), B@15(w=15), C@30(w=15)
+        const result = layout.layout('ABC', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const chars = result.lines[0].chars;
+
+        expect(chars).toHaveLength(3);
+
+        expect(chars[0].xA).toBe(0);
+        expect(chars[0].widthA).toBe(FONT_A_WIDTH);
+        expect(chars[0].xB).toBe(0);
+        expect(chars[0].widthB).toBe(FONT_B_WIDTH);
+
+        expect(chars[1].xA).toBe(FONT_A_WIDTH); // 10
+        expect(chars[1].widthA).toBe(FONT_A_WIDTH);
+        expect(chars[1].xB).toBe(FONT_B_WIDTH); // 15
+        expect(chars[1].widthB).toBe(FONT_B_WIDTH);
+
+        expect(chars[2].xA).toBe(FONT_A_WIDTH * 2); // 20
+        expect(chars[2].xB).toBe(FONT_B_WIDTH * 2); // 30
+    });
+
+    it('returns cached result when called again with same arguments', () => {
+        const r1 = layout.layout('ABC', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const r2 = layout.layout('ABC', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        expect(r2).toBe(r1); // strict reference equality — same object
+    });
+
+    it('re-computes when text changes', () => {
+        const r1 = layout.layout('ABC', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const r2 = layout.layout('DEF', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        expect(r2).not.toBe(r1);
+        expect(r2.lines[0].text).not.toBe(r1.lines[0].text);
+    });
+
+    it('re-computes when width changes', () => {
+        const r1 = layout.layout('Hello World', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const r2 = layout.layout('Hello World', '400 16px "FontA"', '400 16px "FontB"', 60, 20);
+        expect(r2).not.toBe(r1);
+    });
+
+    it('re-computes when fontA changes', () => {
+        const r1 = layout.layout('ABC', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const r2 = layout.layout('ABC', '400 24px "FontA"', '400 16px "FontB"', 500, 20);
+        expect(r2).not.toBe(r1);
+    });
+});