refactoring: arcCosine function test, rename

src/test/test_funktionen.c

@@ -161,7 +161,7 @@ void test_arcSine_for_0_5(void) {
     // Add more test cases for different inputs and expected outputs
 }
 
-void test_arcCosine(void) {
+void test_arcCosine_for_0_5(void) {
     float result = arcCosine(0.5);
     TEST_ASSERT_EQUAL_FLOAT(1.047198, result);
     // Add more test cases for different inputs and expected outputs