1 files changed, 32 insertions, 0 deletions
diff --git a/test/approx_derivative.t.c b/test/approx_derivative.t.c
new file mode 100644
index 0000000..6bcac79
--- /dev/null
+++ b/test/approx_derivative.t.c
@@ -0,0 +1,32 @@
+#include "lizfcm.test.h"
+
+double f(double x) { return x * x; }
+
+double f_prime(double x) { return 2 * x; }
+
+double H = 0.0001;
+double ACCEPTED_DERIVATIVE_ERROR = 0.0001;
+
+UTEST(derivative, central) {
+  double a = 3.0;
+  double expected = f_prime(a);
+  double f_prime_x = central_derivative_at(&f, a, H);
+
+  EXPECT_NEAR(expected, f_prime_x, ACCEPTED_DERIVATIVE_ERROR);
+}
+
+UTEST(derivative, forward) {
+  double a = 3.0;
+  double expected = f_prime(a);
+  double f_prime_x = forward_derivative_at(&f, a, H);
+
+  EXPECT_NEAR(expected, f_prime_x, ACCEPTED_DERIVATIVE_ERROR);
+}
+
+UTEST(derivative, backward) {
+  double a = 3.0;
+  double expected = f_prime(a);
+  double f_prime_x = backward_derivative_at(&f, a, H);
+
+  EXPECT_NEAR(expected, f_prime_x, ACCEPTED_DERIVATIVE_ERROR);
+}