added function to test containment

Containment uses the sumOfTri to determine if a point is inside of the
rectangle, r1.  It checks all four points of r2 (p1, p2, p3, p4) against
r1.  If they are all inside, then the rectangle is contained.

rectangle_test.go

@@ -52,3 +52,46 @@ func TestSize(t *testing.T) {
 
 	}
 }
+
+func TestContainment(t *testing.T) {
+	var containmentTest = []struct {
+		r        []Rectangle
+		expected bool
+	}{
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{1, 1}, Point{1, 2}, Point{2, 1}, Point{2, 2}}},
+			true,
+		},
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{1, 1}, Point{1, 2}, Point{2, 1}, Point{2, 2}}},
+			true,
+		},
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}}},
+			false,
+		},
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{3, 3}, Point{3, 4}, Point{4, 3}, Point{4, 4}}},
+			false,
+		},
+	}
+	for _, rt := range containmentTest {
+		actual := Containment(rt.r[0], rt.r[1])
+		if actual != rt.expected {
+			t.Errorf(
+				"failed spiral:\n\texpected: %d\n\t  actual: %d",
+				rt.expected,
+				actual,
+			)
+		}
+
+	}
+}