diff --git a/pdfminer/utils.py b/pdfminer/utils.py
index 31c608a..1eeefc3 100644
--- a/pdfminer/utils.py
+++ b/pdfminer/utils.py
@@ -161,7 +161,6 @@ def fsplit(pred, objs):
 # drange
 def drange(v0, v1, d):
     """Returns a discrete range."""
-    assert v0 < v1, str((v0, v1, d))
     return range(int(v0)//d, int(v1+d)//d)
 
 
diff --git a/tests/test_utils.py b/tests/test_utils.py
new file mode 100644
index 0000000..e7d9d71
--- /dev/null
+++ b/tests/test_utils.py
@@ -0,0 +1,40 @@
+from nose.tools import assert_equal
+
+from pdfminer.layout import LTComponent
+from pdfminer.utils import make_compat_str, Plane
+
+
+class TestPlane(object):
+    def test_find_nothing_in_empty_bbox(self):
+        plane, _ = self.given_plane_with_one_object()
+        result = list(plane.find((50, 50, 100, 100)))
+        assert_equal(result, [])
+
+    def test_find_nothing_after_removing(self):
+        plane, obj = self.given_plane_with_one_object()
+        plane.remove(obj)
+        result = list(plane.find((0, 0, 100, 100)))
+        assert_equal(result, [])
+
+    def test_find_object_in_whole_plane(self):
+        plane, obj = self.given_plane_with_one_object()
+        result = list(plane.find((0, 0, 100, 100)))
+        assert_equal(result, [obj])
+
+    def test_find_if_object_is_smaller_than_gridsize(self):
+        plane, obj = self.given_plane_with_one_object(object_size=1, gridsize=100)
+        result = list(plane.find((0, 0, 100, 100)))
+        assert_equal(result, [obj])
+
+    def test_find_object_if_much_larger_than_gridsize(self):
+        plane, obj = self.given_plane_with_one_object(object_size=100, gridsize=10)
+        result = list(plane.find((0, 0, 100, 100)))
+        assert_equal(result, [obj])
+
+    @staticmethod
+    def given_plane_with_one_object(object_size=50, gridsize=50):
+        bounding_box = (0, 0, 100, 100)
+        plane = Plane(bounding_box, gridsize)
+        obj = LTComponent((0, 0, object_size, object_size))
+        plane.add(obj)
+        return plane, obj
\ No newline at end of file