Add basic tests for ObjecitiveFun struct

src/objective_function.rs

@@ -82,3 +82,32 @@ impl<T: XVar<E>, E> Fun<T, E> {
         Fun { function, prime }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_eval() {
+        let function = Box::new(|x: &[f64]| -> f64 { x[0] + x[1] });
+        let fun_with_numerical_diff = FunWithNumericalDiff {
+            function,
+            dx: 1e-6,
+            style: DiffStyle::ForwardDifference,
+        };
+        assert_eq!(fun_with_numerical_diff.eval(&vec![1.0, 2.0]), 3.0);
+    }
+
+    #[test]
+    fn test_prime() {
+        let function = Box::new(|x: &[f64]| -> f64 { x[0] + x[1] });
+        let fun_with_numerical_diff = FunWithNumericalDiff {
+            function,
+            dx: 1e-6,
+            style: DiffStyle::ForwardDifference,
+        };
+        let prime = fun_with_numerical_diff.prime(&vec![1.0, 2.0]);
+        assert!(prime[0] - 1.0 < 1e-6);
+        assert!(prime[1] - 1.0 < 1e-6);
+    }
+}