division by zero crashes

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Final diff

diff --git a/calc.py b/calc.py
index f16c6ca..b7d522d 100644
--- a/calc.py
+++ b/calc.py
@@ -15,6 +15,8 @@ def calculate(left: float, operator: str, right: float) -> float:
     if operator == "*":
         return left * right
     if operator == "/":
+        if right == 0:
+            raise CalculatorError("division by zero")
         return left / right
     raise CalculatorError(f"unknown operator: {operator}")
 
diff --git a/test_calc.py b/test_calc.py
index 856b0c9..9930cb5 100644
--- a/test_calc.py
+++ b/test_calc.py
@@ -23,3 +23,31 @@ def test_main_prints_result(capsys):
 def test_main_reports_unknown_operator(capsys):
     assert main(["1", "%", "2"]) == 1
     assert "unknown operator" in capsys.readouterr().err
+
+
+@pytest.mark.parametrize(("left", "right"), [(1, 0), (0, 0)])
+def test_division_by_zero_raises(left, right):
+    with pytest.raises(CalculatorError, match="division by zero"):
+        calculate(left, "/", right)
+
+
+def test_main_reports_division_by_zero(capsys):
+    assert main(["1", "/", "0"]) == 1
+    assert "division by zero" in capsys.readouterr().err
+
+
+@pytest.mark.parametrize("right", [-0.0, 0.0])
+def test_division_by_negative_or_positive_zero_raises(right):
+    with pytest.raises(CalculatorError, match="division by zero"):
+        calculate(5, "/", right)
+
+
+def test_main_reports_division_by_zero_float_spelling(capsys):
+    assert main(["1", "/", "0.0"]) == 1
+    captured = capsys.readouterr()
+    assert "division by zero" in captured.err
+    assert "Traceback" not in captured.err
+
+
+def test_division_by_tiny_nonzero_still_divides():
+    assert calculate(1, "/", 1e-300) == pytest.approx(1e300)