Interval exception detect when modify the lower or the upper property on an exist interval instance

.travis.yml

@@ -1,11 +1,25 @@
 language: python
-python:
-  - 2.7
-  - 3.3
-  - 3.4
-  - 3.5
-  - pypy
-  - pypy3
+matrix:
+    include:
+        - python: 2.7
+          dist: trusty
+          sudo: false
+        - python: 3.3
+          dist: trusty
+          sudo: false
+        - python: 3.4
+          dist: trusty
+          sudo: false
+        - python: 3.5
+          dist: trusty
+          sudo: false
+        - python: pypy
+          dist: trusty
+          sudo: false
+        - python: pypy3
+          dist: trusty
+          sudo: false
+
 install:
   - pip install -e ".[test]"
 script:

intervals/interval.py

@@ -184,15 +184,19 @@ def __init__(
             self.parser(bounds, lower_inc, upper_inc)
         )
 
-        if self.lower > self.upper:
+        self.range_init_and_setter_exception_detect(self.lower, self.upper, self.lower_inc, self.upper_inc)
+
+    @classmethod
+    def range_init_and_setter_exception_detect(cls, lower, upper, lower_inc, upper_inc):
+        if lower > upper:
             raise RangeBoundsException(
-                self.lower,
-                self.upper
+                lower,
+                upper
             )
         if (
-            self.lower == self.upper and
-            not self.lower_inc and
-            not self.upper_inc
+            lower == upper and
+            not lower_inc and
+            not upper_inc
         ):
             raise IllegalArgument(
                 'The bounds may be equal only if at least one of the bounds '
@@ -320,8 +324,13 @@ def lower(self):
     def lower(self, value):
         value = self.coerce_value(value)
         if value is None:
+            if hasattr(self, 'upper_inc'):
+                self.range_init_and_setter_exception_detect(-inf, self.upper, self.lower_inc, self.upper_inc)
             self._lower = -inf
         else:
+            if hasattr(self, 'upper_inc'):
+                self.range_init_and_setter_exception_detect(self.round_value_by_step(value), self.upper, self.lower_inc,
+                                                            self.upper_inc)
             self._lower = self.round_value_by_step(value)
 
     @property
@@ -332,8 +341,13 @@ def upper(self):
     def upper(self, value):
         value = self.coerce_value(value)
         if value is None:
+            if hasattr(self, 'upper_inc'):
+                self.range_init_and_setter_exception_detect(self.lower, inf, self.lower_inc, self.upper_inc)
             self._upper = inf
         else:
+            if hasattr(self, 'upper_inc'):
+                self.range_init_and_setter_exception_detect(self.lower, self.round_value_by_step(value), self.lower_inc,
+                                                            self.upper_inc)
             self._upper = self.round_value_by_step(value)
 
     def round_value_by_step(self, value):

tests/interval/test_initialization.py

@@ -202,3 +202,47 @@ class TestTypeGuessing(object):
     )
     def test_guesses_types(self, number_range, type):
         assert Interval(number_range).type == type
+
+
+class TestIntervalChanging(object):
+    @mark.parametrize(
+        ('constructor', 'number_range', 'bad_lower'),
+        (
+            (IntInterval, (1, 2), 3),
+            (IntInterval, [1, 2], 3),
+            (IntInterval, (1, 2), float('inf')),
+            (CharacterInterval, ('a', 'b'), 'c'),
+            (CharacterInterval, ('a', 'b'), 'd'),
+            (CharacterInterval, ('a', 'b'), inf),
+        )
+    )
+    def test_raises_exception_for_badly_lower_changing(
+        self,
+        constructor,
+        number_range,
+        bad_lower
+    ):
+        with raises(RangeBoundsException):
+            interval = constructor(number_range)
+            interval.lower = bad_lower
+
+    @mark.parametrize(
+        ('constructor', 'number_range', 'bad_upper'),
+        (
+            (IntInterval, (1, 2), 0),
+            (IntInterval, [1, 2], 0),
+            (IntInterval, (1, 2), float('-inf')),
+            (CharacterInterval, ('b', 'c'), 'a'),
+            (CharacterInterval, ('b', 'd'), 'a'),
+            (CharacterInterval, ('b', 'c'), -inf),
+        )
+    )
+    def test_raises_exception_for_badly_upper_changing(
+        self,
+        constructor,
+        number_range,
+        bad_upper
+    ):
+        with raises(RangeBoundsException):
+            interval = constructor(number_range)
+            interval.upper = bad_upper