Add 3 new modes of calculation

calc/calc.go

@@ -5,7 +5,13 @@ type Calculator interface {
 }
 
 type Addition struct{}
+type Subtraction struct{}
+type Multiplication struct{}
+type Division struct{}
 
 func (Addition) Calculate(a, b int) int {
 	return a + b
 }
+func (Subtraction) Calculate(a, b int) int    { return a - b }
+func (Multiplication) Calculate(a, b int) int { return a * b }
+func (Division) Calculate(a, b int) int       { return a / b }

calc/calc_test.go

@@ -1,6 +1,8 @@
 package calc
 
-import "testing"
+import (
+	"testing"
+)
 
 func TestAddition_Calculate(t *testing.T) {
 	type args struct {
@@ -36,6 +38,30 @@ func TestAddition(t *testing.T) {
 
 }
 
+func TestSubtraction(t *testing.T) {
+	var calculator Subtraction
+	assertEqual(t, 0, calculator.Calculate(0, 0))
+	assertEqual(t, 1, calculator.Calculate(0, -1))
+	assertEqual(t, 2, calculator.Calculate(4, 2))
+	assertEqual(t, -4, calculator.Calculate(0, 4))
+}
+
+func TestMultiplication(t *testing.T) {
+	var calculator Multiplication
+	assertEqual(t, 0, calculator.Calculate(0, 0))
+	assertEqual(t, 0, calculator.Calculate(0, -1))
+	assertEqual(t, 8, calculator.Calculate(4, 2))
+	assertEqual(t, 0, calculator.Calculate(0, 4))
+}
+
+func TestDivision(t *testing.T) {
+	var calculator Division
+	assertEqual(t, 1, calculator.Calculate(1, 1))
+	assertEqual(t, 0, calculator.Calculate(0, -1))
+	assertEqual(t, 2, calculator.Calculate(4, 2))
+	assertEqual(t, -4, calculator.Calculate(16, -4))
+}
+
 func assertEqual(t *testing.T, expected, actual any) {
 	if actual != expected {
 		t.Helper() //so that the stack trace shows the actual test that failed

main_test.go

@@ -6,8 +6,8 @@ import (
 	"reflect"
 	"testing"
 
-	"calc-lib/calc"
-	"calc-lib/handler"
+	calc "calc-lib/calc"
+	handler "calc-lib/handler"
 )
 
 func assertEqual(t *testing.T, expected, actual any) {