refactor: stress ratio calculations

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,19 +1,19 @@
-## Does this PR introduce a breaking change?
+## Does this pull request introduce a breaking change?
 - [ ] Yes
 - [ ] No
 
 <!-- If yes, describe the impact and migration path below. -->
 
-## Describe the purpose of this pull request.
+## Purpose of this pull request
 
 
-## Describe how this was implemented.
+## Benefits of the pull request
 
 
-## Describe any particular area(s) reviewers should focus on.
+## Any particular area(s) reviewers should focus on
 
 
-## Provide any other pertinent information.
+## Any other pertinent information
 <!-- Provide any other information that is import to this PR such as
 screenshots if this impacts the GUI. -->
 

src/ramstk/analyses/stress.py

@@ -1,9 +1,9 @@
 # -*- coding: utf-8 -*-
 #
-#       ramstk.analyses.Stress.py is part of the RAMSTK Project
+#       ramstk.analyses.stress.py is part of the RAMSTK Project
 #
 # All rights reserved.
-# Copyright 2019 Doyle Rowland doyle.rowland <AT> reliaqual <DOT> com
+# Copyright since 2007 Doyle Rowland doyle.rowland <AT> reliaqual <DOT> com
 """Component Stress Calculations Module."""
 
 
@@ -21,23 +21,22 @@ def calculate_stress_ratio(stress_operating, stress_rated):
     >>> calculate_stress_ratio(1, 1.29)
     0.7751937984496123
 
-    Rated stress must not be zero:
-    >>> calculate_stress_ratio(0.382, 0.0)
-    Traceback (most recent call last):
-        ...
-    ZeroDivisionError: float division by zero
-
-    Stress inputs must not be strings:
-    >>>  calculate_stress_ratio(0.382, '3.2')
-    Traceback (most recent call last):
-        ...
-    TypeError: unsupported operand type(s) for /: 'float' and 'str'
-
     :param stress_operating: the device's operating level of the stress.
     :param stress_rated: the devices's rated stress.
-    :return: _stress_ratio; the ratio of operating stress to rated stress.
+    :return: the ratio of operating stress to rated stress.
     :rtype: float
     :raise: TypeError if an input value is non-numerical.
     :raise: ZeroDivisionError if the rated stress is zero.
     """
+    if not isinstance(stress_operating, (int, float)) or not isinstance(
+        stress_rated, (int, float)
+    ):
+        raise TypeError("Inputs must be numerical (int or float).")
+
+    if stress_operating < 0 or stress_rated < 0:
+        raise ValueError("Stress values must be non-negative.")
+
+    if stress_rated == 0:
+        raise ZeroDivisionError("Rated stress must not be zero.")
+
     return stress_operating / stress_rated

tests/analyses/test_stress.py

@@ -5,7 +5,7 @@
 #       tests.analyses.test_stress.py is part of The RAMSTK Project
 #
 # All rights reserved.
-# Copyright 2019 Doyle Rowland doyle.rowland <AT> reliaqual <DOT> com
+# Copyright since 2007 Doyle Rowland doyle.rowland <AT> reliaqual <DOT> com
 """Test class for the electrical stress module."""
 
 # Third Party Imports
@@ -21,7 +21,7 @@ def test_calculate_stress_ratio():
     """Return a float stress ratio on success."""
     _stress_ratio = stress.calculate_stress_ratio(0.625, 1.25)
 
-    assert pytest.approx(_stress_ratio) == 0.5
+    assert _stress_ratio == pytest.approx(0.5)
 
 
 @pytest.mark.unit
@@ -38,3 +38,35 @@ def test_calculate_stress_ratio_zero_rated():
     """Raise a ZeroDivisionError if passed a rated stress of zero."""
     with pytest.raises(ZeroDivisionError):
         stress.calculate_stress_ratio(0.625, 0.0)
+
+
+@pytest.mark.unit
+@pytest.mark.calculation
+def test_calculate_stress_ratio_negative_operating():
+    """Raise a ValueError if passed a negative operating stress."""
+    with pytest.raises(ValueError):
+        stress.calculate_stress_ratio(-0.625, 1.25)
+
+
+@pytest.mark.unit
+@pytest.mark.calculation
+def test_calculate_stress_ratio_negative_rated():
+    """Raise a ValueError if passed a negative rated stress."""
+    with pytest.raises(ValueError):
+        stress.calculate_stress_ratio(0.625, -1.25)
+
+
+@pytest.mark.unit
+@pytest.mark.calculation
+def test_calculate_stress_ratio_zero_operating():
+    """Return 0.0 when operating stress is zero."""
+    _stress_ratio = stress.calculate_stress_ratio(0.0, 1.25)
+    assert _stress_ratio == pytest.approx(0.0)
+
+
+@pytest.mark.unit
+@pytest.mark.calculation
+def test_calculate_stress_ratio_both_zero():
+    """Raise a ZeroDivisionError if both operating and rated stresses are zero."""
+    with pytest.raises(ZeroDivisionError):
+        stress.calculate_stress_ratio(0.0, 0.0)