AP_Math: added test for SCurve::calculate_path

this was the values shown in the core dump for failing guided mode
test in CI

libraries/AP_Math/tests/test_scurve.cpp

@@ -0,0 +1,21 @@
+#include <AP_gtest.h>
+
+#include <AP_Math/AP_Math.h>
+#include <AP_Math/vector2.h>
+#include <AP_Math/vector3.h>
+#include <AP_Math/SCurve.h>
+
+TEST(LinesScurve, test_calculate_path)
+{
+    float Jm_out, t2_out, t4_out, t6_out;
+    SCurve::calculate_path(0.300000012, 19.4233513, 0, 5.82700586, 188.354691, 2.09772229,
+                           Jm_out, t2_out, t4_out, t6_out);
+    EXPECT_FLOAT_EQ(Jm_out, 19.423351);
+    EXPECT_FLOAT_EQ(t2_out, 0.0);
+    EXPECT_FLOAT_EQ(t4_out, 0.0);
+    EXPECT_FLOAT_EQ(t6_out, 0.0);
+}
+
+
+AP_GTEST_MAIN()
+int hal = 0; //weirdly the build will fail without this