[orx-gradient] Move DescribeSpec based tests to jvmTest

orx-gradient-descent/src/jvmTest/kotlin/TestGradient.kt

@@ -0,0 +1,41 @@
+import io.kotest.core.spec.style.DescribeSpec
+import io.kotest.matchers.equals.shouldBeEqual
+import org.openrndr.extra.gradientdescent.gradient
+
+class TestGradient : DescribeSpec({
+    describe("a simple 1d function") {
+        fun parabola(x: DoubleArray): Double {
+            return x[0] * x[0]
+        }
+        it("its gradient at x=0 is 0.0") {
+            val g0 = gradient(doubleArrayOf(0.0), ::parabola)
+            g0.size.shouldBeEqual(1)
+            g0[0].shouldBeEqual(0.0)
+        }
+        it("its gradient at x=1 is ~2.0") {
+            val g1 = gradient(doubleArrayOf(1.0), ::parabola)
+        }
+        it("its gradient at x=-1 is ~-2.0") {
+            val g1 = gradient(doubleArrayOf(-1.0), ::parabola)
+        }
+    }
+
+    describe("a simple 2d function") {
+        fun parabola(x: DoubleArray): Double {
+            return x[0] * x[0] + x[1] * x[1]
+        }
+
+        it("its gradient at x=0 is 0.0") {
+            val g0 = gradient(doubleArrayOf(0.0, 0.0), ::parabola)
+            g0.size.shouldBeEqual(2)
+            g0[0].shouldBeEqual(0.0)
+        }
+
+        it("its gradient at x=1 is ~2.0") {
+            val g1 = gradient(doubleArrayOf(1.0, 1.0), ::parabola)
+        }
+        it("its gradient at x=-1 is ~-2.0") {
+            val g1 = gradient(doubleArrayOf(-1.0, -1.0), ::parabola)
+        }
+    }
+})