Added unittest for exponentialFunction

src/test/c/test_taschenrechner.c

@@ -150,5 +150,10 @@ void test_logarithmBase2Function(void) {
     TEST_ASSERT_EQUAL_FLOAT(3.0, logarithmBase2Function(8.0));
 }
 
+// Exponential function
+void test_exponentialFunction(void) {
+    // Your test code here
+    TEST_ASSERT_EQUAL_FLOAT(1.0, exponentialFunction(0.0));
+}
 
 #endif // TEST