refactoring: consine function test, rename

src/test/test_funktionen.c

@@ -143,7 +143,7 @@ void test_sine_for_0_5(void) {
     TEST_ASSERT_EQUAL_FLOAT(0.479426, result);
 }
 
-void test_cosine(void) {
+void test_cosine_for_1(void) {
     float result = cosine(1.0);
     TEST_ASSERT_EQUAL_FLOAT(0.540302, result);
     // Add more test cases for different inputs and expected outputs