add test case for equatorial orbit

tests/orbit_test.cpp

@@ -79,6 +79,21 @@ TEST_CASE("state vectors to orbital elements, example 3.1", "[orbits]")
 	REQUIRE_THAT(el.nu, WithinAbs(orbitClampAngle(DEG2RAD(280)), 1));
 }
 
+TEST_CASE("elements to state vectors, edge case equatorial orbit", "[orbits]")
+{
+	double mu = EARTH_GRAVITATIONAL_PARAMETER;
+	dvec3 r = dvec3(0, -8000, 0);
+	dvec3 v = dvec3(7.45, 0, 0);
+
+	OrbitalElements el = orbitGetElementsFromStateVectors(r, v, mu);
+	REQUIRE_THAT(el.a, WithinAbs(9028.776, 1e-3));
+	REQUIRE_THAT(el.e, WithinAbs(0.114, 1e-3));
+	REQUIRE_THAT(el.iota, WithinAbs(0.0, 1e-3));
+	REQUIRE_THAT(el.ohm, WithinAbs(0.0, 1e-3));
+	REQUIRE_THAT(el.omega, WithinAbs(-1.571, 1e-3));
+	REQUIRE_THAT(el.nu, WithinAbs(0.0, 1e-3));
+}
+
 TEST_CASE("orbital elements to state vectors, example 3.2", "[orbits]")
 {
 	double a = MOLNIYA_SEMI_MAJOR_AXIS;