diff --git a/kmath/rat.py b/kmath/rat.py
index 226dd6d..d202c27 100644
--- a/kmath/rat.py
+++ b/kmath/rat.py
@@ -1,5 +1,7 @@
 import math
 
+import numpy
+
 
 class Rational:
     """
@@ -39,7 +41,7 @@ class Rational:
         return Rational(self.n * other.d, self.d * other.n)
 
     def lcm(self, other):
-        return int(math.lcm(self.d, other.d))
+        return int(numpy.lcm(self.d, other.d))
 
     def normalize(self, other):
         lcm = self.lcm(other)
@@ -107,6 +109,7 @@ def ipow(n, m):
 
     while m > 1:
         x = x * n
+        m -= 1
 
     return x
 
diff --git a/tests/linea.py b/tests/linea.py
index 1f64dce..3f8d25f 100644
--- a/tests/linea.py
+++ b/tests/linea.py
@@ -1,3 +1,5 @@
+import sys
+
 import numpy
 import pytest
 
@@ -165,3 +167,7 @@ def test_cross_product():
     v7 = vec.Vector(-6.007, 0.124, 5.772)
     area = 42.565
     assert fequal(vec.area_triangle(v6, v7), area)
+
+
+if __name__ == '__main__':
+    sys.exit(pytest.main(["-qq"]))
diff --git a/tests/rat.py b/tests/rat.py
new file mode 100644
index 0000000..d603639
--- /dev/null
+++ b/tests/rat.py
@@ -0,0 +1,81 @@
+import sys
+
+import pytest
+
+import kmath.rat as rat
+
+
+def test_add():
+    r1 = rat.Rational(1, 1)
+    r2 = rat.Int(3)
+    r3 = r1 + r2
+    assert r3.n == 4
+    assert r3.d == 1
+    assert float(r3) == 4.0
+    assert int(r3) == 4
+
+
+def test_mul():
+    r1 = rat.Rational(1, 2)
+    r2 = rat.Rational(1, 8)
+    r3 = rat.Rational(1, 16)
+    assert r1 * r2 == r3
+
+
+def test_div():
+    r1 = rat.Rational(1, 2)
+    r2 = rat.Rational(1, 8)
+    r3 = rat.Int(4)
+    assert r1 / r2 == r3
+
+
+def test_pow():
+    r1 = rat.Rational(1, 2)
+    r2 = rat.Rational(3, 4)
+    r3 = rat.Rational(1, 4)
+    r4 = rat.Rational(9, 16)
+    r5 = rat.Rational(1, 8)
+    assert r1 ** 2 == r3
+    assert r2 ** 2 == r4
+    assert rat.ipow(r1, 3) == r5
+
+
+def test_scale():
+    r1 = rat.Rational(1, 2)
+    r2 = rat.Rational(2, 4)
+    assert r1.scale(2) == r2
+    assert r1.scale(2).reduce() == r1
+
+
+def test_dbz_protection():
+    assert rat.Rational(0, 0) == rat.Rational(1, 0)
+
+
+def test_equality():
+    r1 = rat.Rational(1, 2)
+    r2 = rat.Rational(3, 4)
+    r3 = rat.Rational(2, 4)
+
+    assert r1 < r2
+    assert r3 < r2
+    assert r1 <= r3
+    assert r1 == r3
+    assert r2 > r1
+    assert r2 >= r3
+
+
+def test_sub():
+    r1 = rat.Rational(1, 2)
+    r2 = rat.Rational(1, 8)
+    r3 = rat.Rational(3, 8)
+    assert r1 - r2 == r3
+
+
+def test_recurse():
+    """test from the calculus course"""
+    r = rat.Rational(239, 169)
+    assert rat.recurse(5) == r
+
+
+if __name__ == '__main__':
+    sys.exit(pytest.main(["-qq"]))