Fix week of month calculation (#446)

Author: sdispater

pendulum/date.py

@@ -76,7 +76,9 @@ def days_in_month(self):
 
     @property
     def week_of_month(self):
-        return int(math.ceil(self.day / DAYS_PER_WEEK))
+        first_day_of_month = self.replace(day=1)
+
+        return self.week_of_year - first_day_of_month.week_of_year + 1
 
     @property
     def age(self):

tests/date/test_getters.py

@@ -52,10 +52,13 @@ def test_is_long_year():
 
 def test_week_of_month():
     assert pendulum.Date(2012, 9, 30).week_of_month == 5
-    assert pendulum.Date(2012, 9, 28).week_of_month == 4
-    assert pendulum.Date(2012, 9, 20).week_of_month == 3
+    assert pendulum.Date(2012, 9, 28).week_of_month == 5
+    assert pendulum.Date(2012, 9, 20).week_of_month == 4
     assert pendulum.Date(2012, 9, 8).week_of_month == 2
     assert pendulum.Date(2012, 9, 1).week_of_month == 1
+    assert pendulum.date(2020, 1, 1).week_of_month == 1
+    assert pendulum.date(2020, 1, 7).week_of_month == 2
+    assert pendulum.date(2020, 1, 14).week_of_month == 3
 
 
 def test_week_of_year_first_week():

tests/datetime/test_getters.py

@@ -185,10 +185,13 @@ def test_is_long_year():
 
 def test_week_of_month():
     assert pendulum.datetime(2012, 9, 30).week_of_month == 5
-    assert pendulum.datetime(2012, 9, 28).week_of_month == 4
-    assert pendulum.datetime(2012, 9, 20).week_of_month == 3
+    assert pendulum.datetime(2012, 9, 28).week_of_month == 5
+    assert pendulum.datetime(2012, 9, 20).week_of_month == 4
     assert pendulum.datetime(2012, 9, 8).week_of_month == 2
     assert pendulum.datetime(2012, 9, 1).week_of_month == 1
+    assert pendulum.datetime(2020, 1, 1).week_of_month == 1
+    assert pendulum.datetime(2020, 1, 7).week_of_month == 2
+    assert pendulum.datetime(2020, 1, 14).week_of_month == 3
 
 
 def test_week_of_year_first_week():