Adding upstream version 2.1.2.

Signed-off-by: Daniel Baumann <daniel@debian.org>

polynomial_regression_test.go

@@ -0,0 +1,35 @@
+package chart
+
+import (
+	"testing"
+
+	"github.com/wcharczuk/go-chart/v2/matrix"
+	"github.com/wcharczuk/go-chart/v2/testutil"
+)
+
+func TestPolynomialRegression(t *testing.T) {
+	// replaced new assertions helper
+
+	var xv []float64
+	var yv []float64
+
+	for i := 0; i < 100; i++ {
+		xv = append(xv, float64(i))
+		yv = append(yv, float64(i*i))
+	}
+
+	values := ContinuousSeries{
+		XValues: xv,
+		YValues: yv,
+	}
+
+	poly := &PolynomialRegressionSeries{
+		InnerSeries: values,
+		Degree:      2,
+	}
+
+	for i := 0; i < 100; i++ {
+		_, y := poly.GetValues(i)
+		testutil.AssertInDelta(t, float64(i*i), y, matrix.DefaultEpsilon)
+	}
+}