diff --git a/test/test_reihen.c b/test/test_reihen.c
index f75c8fa..a020dec 100644
--- a/test/test_reihen.c
+++ b/test/test_reihen.c
@@ -73,4 +73,23 @@ void test_sin(void){
     TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.0, r4);
 }
 
+void test_cos(void){
+    double r1, r2, r3, r4;
+
+    r1 = cosD(50.0);
+    r2 = cosD(90.0);
+    r3 = cosD(36.97);
+    r4 = cosD(180.0);
+
+    printf("%lf\n", r1);
+    printf("%lf\n", r2);
+    printf("%lf\n", r3);
+    printf("%lf\n", r4);
+
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.642787, r1);
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.0, r2);
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.798950, r3);
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, -1.0, r4);
+}
+
 #endif // TEST
\ No newline at end of file