add tests for radians function

src/reihen.c

@@ -38,7 +38,7 @@ double squashDegreesTo360(double x){
 }
 
 double radians(double d){
-    return d / PI * 180;
+    return d * PI / 180;
 }
 
 double pi(double eps){

src/reihen.h

@@ -4,5 +4,6 @@
 double exponential(double x);
 double euler();
 double pi();
+double radians(double d);
 
 #endif // reihen.h

test/test_reihen.c

@@ -44,4 +44,23 @@ void test_pi(void){
     TEST_ASSERT_DOUBLE_WITHIN(0.0000001, 3.14159265, r1);
 }
 
+void test_degrees_to_radians(){
+    double r1, r2, r3, r4;
+
+    r1 = radians(90.0);
+    r2 = radians(180.0);
+    r3 = radians(51.6);
+    r4 = radians(36.97);
+
+    printf("%lf\n", r1);
+    printf("%lf\n", r2);
+    printf("%lf\n", r3);
+    printf("%lf\n", r4);
+
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 1.570796, r1);
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, pi(1e-8), r2);
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.900589, r3);
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.645248, r4);
+}
+
 #endif // TEST