shapes: add Circle struct and Area func

shapes/shapes.go

@@ -1,10 +1,16 @@
 package shapes
 
+import "math"
+
 type Rectangle struct {
 	Width  float64
 	Height float64
 }
 
+type Circle struct {
+	Radius float64
+}
+
 func (r Rectangle) Perimeter() float64 {
 	return 2 * (r.Width + r.Height)
 }
@@ -12,3 +18,7 @@ func (r Rectangle) Perimeter() float64 {
 func (r Rectangle) Area() float64 {
 	return r.Width * r.Height
 }
+
+func (c Circle) Area() float64 {
+	return c.Radius * c.Radius * math.Pi
+}

shapes/shapes_test.go

@@ -23,13 +23,13 @@ func TestArea(t *testing.T) {
 		}
 	})
 
-	// t.Run("circles", func(t *testing.T) {
-	// 	circle := Circle{10}
-	// 	got := Area(circle)
-	// 	exp := 314.1592653589793
-	//
-	// 	if got != exp {
-	// 		t.Errorf("got %.2f expected %.2f", got, exp)
-	// 	}
-	// })
+	t.Run("circles", func(t *testing.T) {
+		circle := Circle{10}
+		got := circle.Area()
+		exp := 314.1592653589793
+
+		if got != exp {
+			t.Errorf("got %.2f expected %.2f", got, exp)
+		}
+	})
 }