Fixed exact value atol bug for negative values

Author: jmafoster1

causal_testing/testing/causal_test_outcome.py

@@ -77,9 +77,11 @@ class ExactValue(SomeEffect):
     def __init__(self, value: float, atol: float = None):
         self.value = value
         if atol is None:
-            self.atol = value * 0.05
+            self.atol = abs(value * 0.05)
         else:
             self.atol = atol
+        if self.atol < 0:
+            raise ValueError("Tolerance must be an absolute value.")
 
     def apply(self, res: CausalTestResult) -> bool:
         if res.ci_valid():

tests/testing_tests/test_causal_test_outcome.py

@@ -189,6 +189,10 @@ def test_exactValue_fail(self):
         ev = ExactValue(5, 0.1)
         self.assertFalse(ev.apply(ctr))
 
+    def test_invalid_atol(self):
+        with self.assertRaises(ValueError):
+            ExactValue(5, -0.1)
+
     def test_invalid(self):
         test_value = TestValue(type="invalid", value=5.05)
         ctr = CausalTestResult(