Add Unicode math formatter tests

tests/test_math_format.py

@@ -0,0 +1,24 @@
+import pytest
+
+from ai_typewriter.math_format import format_math_text
+
+
+def test_plain_mode_keeps_linear_math_literal():
+    assert format_math_text("z_1 + x^2", "plain") == "z_1 + x^2"
+
+
+def test_unicode_mode_converts_indices_exponents_and_symbols():
+    result = format_math_text(r"z_1 + x^2 + x_(i+1) + \alpha + \infty", "unicode")
+
+    assert result == "z₁ + x² + xᵢ₊₁ + α + ∞"
+
+
+def test_unicode_mode_converts_common_operators():
+    result = format_math_text(r"\int_0^1 f(x) dx \leq \sum_(k=1)^n a_k", "unicode")
+
+    assert result == "∫₀¹ f(x) dx ≤ ∑ₖ₌₁ⁿ aₖ"
+
+
+def test_invalid_math_text_format_is_rejected():
+    with pytest.raises(ValueError):
+        format_math_text("x_1", "bad")