Reject zero and invalid running times before calculating speed

docs/internal/known-issues.md

@@ -9,7 +9,9 @@ which also covers deliberate non-goals.
 
 **3 open:** 2 medium, 1 low.
 
-## 1. A total time of zero divides by zero and exits with a traceback
+## 1. A total time of zero divides by zero and exits with a traceback — RESOLVED
+
+**Resolution:** Re-prompt for zero or negative total time, negative values, and non-finite input before calculating speed.
 
 **Severity:** Medium
 **Where:** `main.py` -> `main`, `metersps = distance / time`

main.py

@@ -7,6 +7,7 @@
 
 # Running Calculator
 import sys
+import math
 
 
 def calculate_distance(distance, unit):
@@ -159,6 +160,11 @@ def main():
                     input("How many minutes did it take you? (if < 1, enter 0) ")
                 )
                 secs = float(input("How many seconds did it take you? "))
+                if (not math.isfinite(length) or not math.isfinite(secs)
+                        or min(length, hours, mins, secs) < 0
+                        or hours * 3600 + mins * 60 + secs <= 0):
+                    print("Use nonnegative values and a total time greater than zero.")
+                    time_run = True
             except ValueError:
                 print(
                     "Values must be in numerical form, "

tests/test_main.py

@@ -5,9 +5,11 @@
 import sys
 import os
 
+import pytest
+
 sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
-from main import calculate_distance, display_result
+from main import calculate_distance, display_result, main
 
 
 def test_calculate_distance():
@@ -40,3 +42,14 @@ def test_display_result(capsys):
     assert (
         "Your speed was 10 meters per second or 36 kilometers per hour." in captured.out
     )
+
+
+def test_zero_time_reprompts_and_valid_input_still_calculates(monkeypatch, capsys):
+    """Recover from a zero time and calculate the corrected speed."""
+    answers = iter(["meters", "1000", "0", "0", "0", "1000", "0", "1", "0", "quit"])
+    monkeypatch.setattr("builtins.input", lambda _: next(answers))
+    with pytest.raises(SystemExit):
+        main()
+    output = capsys.readouterr().out
+    assert "total time greater than zero" in output
+    assert "16.67 meters per second" in output