added opc example (package)

README.md

@@ -7,7 +7,9 @@ Grokking Go Fundamentals with Tests Video Series / Course
 - [A new learning way on how to write "Hello, World!" program in Go](https://www.youtube.com/watch?v=EECXgocw4N0)
   - [Source Code (helloworld)](./helloworld/)
 - [Everything You Need to Know to Start Writing Tests In Go With TDD (For Go Beginners)](https://www.youtube.com/watch?v=Fr9xox_soKQ&t=794s)
-  - [Source Code](./calculator/)
+  - [Source Code (calculator)](./calculator/)
+- [Let's learn variables and constants in Go with tests and TDD. Part 1](https://www.youtube.com/watch?v=9bny23btS2s&t=422s)
+  - [Source Code (opc)](./opc/)
 
 [Link on YouTube Playlist](https://www.youtube.com/playlist?list=PLCqcI2Ic-eM_4ma__dXm4xX3P9fgQ2V9C)
 

opc/opc.go

@@ -0,0 +1,23 @@
+package opc
+
+import "fmt"
+
+const discountRate float64 = 0.9
+
+func CalculateOrderPrice(
+  itemPrice float64,
+  quantity int,
+  taxRate float64,
+  discount bool,
+) string {
+  totalPrice := itemPrice * float64(quantity)
+
+  if discount {
+    totalPrice = totalPrice * discountRate
+  }
+
+  taxAmount := totalPrice * taxRate
+  finalPrice := totalPrice + taxAmount
+
+  return fmt.Sprintf("The final price is: €%.2f", finalPrice)
+}

opc/opc_test.go

@@ -0,0 +1,56 @@
+package opc_test
+
+import (
+	"go-sandbox/opc"
+	"testing"
+  "fmt"
+)
+
+func TestCalculateOrderPrice(t *testing.T) {
+  type testCase struct {
+    itemPrice, taxRate float64
+    quantity int
+    discount bool
+    want string
+  }
+
+  testCases := []testCase{
+    {
+      itemPrice: 2.99,
+      taxRate: 0.07,
+      quantity: 3,
+      discount: true,
+      want: "The final price is: €8.64",
+    },
+    {
+      itemPrice: 2.99,
+      taxRate: 0.07,
+      quantity: 3,
+      discount: false,
+      want: "The final price is: €9.60",
+    },
+  }
+
+  for _, tc := range testCases {
+    tcName := fmt.Sprintf(
+      "itemPrice = %.2f, quantity = %d, taxRate = %.2f, discount = %t",
+      tc.itemPrice,
+      tc.quantity,
+      tc.taxRate,
+      tc.discount,
+    )
+
+    t.Run(tcName, func (t *testing.T)  {
+      got := opc.CalculateOrderPrice(
+        tc.itemPrice,
+        tc.quantity,
+        tc.taxRate,
+        tc.discount,
+      )
+
+      if tc.want != got {
+        t.Errorf("Failed! Wanted %q, got %q", tc.want, got)
+      }
+    })
+  }
+}