diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4ebc8ae
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+coverage
diff --git a/app/Application.go b/app/Application.go
new file mode 100644
index 0000000..7e040e7
--- /dev/null
+++ b/app/Application.go
@@ -0,0 +1,7 @@
+package app
+
+import "pjm.dev/mock/calculator"
+
+type Application struct {
+	Calculator calculator.Calculatorer
+}
diff --git a/app/CoolAlgorithm.go b/app/CoolAlgorithm.go
new file mode 100644
index 0000000..d5026c6
--- /dev/null
+++ b/app/CoolAlgorithm.go
@@ -0,0 +1,12 @@
+package app
+
+func (application *Application) CoolAlgorithm(x int) int {
+	var output int = x
+
+	output = application.Calculator.Add(output, 0)
+	output = application.Calculator.Subtract(output, 0)
+	output = application.Calculator.Multiply(output, 1)
+	output = application.Calculator.Divide(output, 1)
+
+	return output
+}
diff --git a/app/CoolAlgorithm_test.go b/app/CoolAlgorithm_test.go
new file mode 100644
index 0000000..ca7b78c
--- /dev/null
+++ b/app/CoolAlgorithm_test.go
@@ -0,0 +1,45 @@
+package app_test
+
+import (
+	"testing"
+
+	"go.uber.org/mock/gomock"
+	"pjm.dev/mock/app"
+	"pjm.dev/mock/mock_calculator"
+)
+
+func TestCoolAlgorithm(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	mockCalculator := mock_calculator.NewMockCalculatorer(ctrl)
+
+	number := 100
+
+	mockCalculator.
+		EXPECT().
+		Add(number, 0).
+		Times(1).
+		Return(number)
+
+	mockCalculator.
+		EXPECT().
+		Subtract(number, 0).
+		Times(1).
+		Return(number)
+
+	mockCalculator.
+		EXPECT().
+		Multiply(number, 1).
+		Times(1).
+		Return(number)
+
+	mockCalculator.
+		EXPECT().
+		Divide(number, 1).
+		Times(1).
+		Return(number)
+
+	application := app.Application{Calculator: mockCalculator}
+	if application.CoolAlgorithm(number) != number {
+		t.Fail()
+	}
+}
diff --git a/calculator/Calculatorer.go b/calculator/Calculatorer.go
new file mode 100644
index 0000000..9ca8ab1
--- /dev/null
+++ b/calculator/Calculatorer.go
@@ -0,0 +1,8 @@
+package calculator
+
+type Calculatorer interface {
+	Add(int, int) int
+	Subtract(int, int) int
+	Multiply(int, int) int
+	Divide(int, int) int
+}
diff --git a/calculator/Client.go b/calculator/Client.go
new file mode 100644
index 0000000..6aaa666
--- /dev/null
+++ b/calculator/Client.go
@@ -0,0 +1,19 @@
+package calculator
+
+type Client struct{}
+
+func (client *Client) Add(a int32, b int32) int32 {
+	panic("Can't call this in unit tests!")
+}
+
+func (client *Client) Subtract(a int32, b int32) int32 {
+	panic("Can't call this in unit tests!")
+}
+
+func (client *Client) Multiply(a int32, b int32) int32 {
+	panic("Can't call this in unit tests!")
+}
+
+func (client *Client) Divide(a int32, b int32) int32 {
+	panic("Can't call this in unit tests!")
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..0ccf459
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module pjm.dev/mock
+
+go 1.21.1
+
+require go.uber.org/mock v0.3.0
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..fd2f035
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+go.uber.org/mock v0.3.0 h1:3mUxI1No2/60yUYax92Pt8eNOEecx2D3lcXZh2NEZJo=
+go.uber.org/mock v0.3.0/go.mod h1:a6FSlNadKUHUa9IP5Vyt1zh4fC7uAwxMutEAscFbkZc=
diff --git a/mock_calculator/Client.go b/mock_calculator/Client.go
new file mode 100644
index 0000000..c34526e
--- /dev/null
+++ b/mock_calculator/Client.go
@@ -0,0 +1,94 @@
+// Code generated by MockGen. DO NOT EDIT.
+// Source: ./calculator/Calculatorer.go
+//
+// Generated by this command:
+//
+//	mockgen -source=./calculator/Calculatorer.go -destination=./mock_calculator/Client.go
+//
+// Package mock_calculator is a generated GoMock package.
+package mock_calculator
+
+import (
+	reflect "reflect"
+
+	gomock "go.uber.org/mock/gomock"
+)
+
+// MockCalculatorer is a mock of Calculatorer interface.
+type MockCalculatorer struct {
+	ctrl     *gomock.Controller
+	recorder *MockCalculatorerMockRecorder
+}
+
+// MockCalculatorerMockRecorder is the mock recorder for MockCalculatorer.
+type MockCalculatorerMockRecorder struct {
+	mock *MockCalculatorer
+}
+
+// NewMockCalculatorer creates a new mock instance.
+func NewMockCalculatorer(ctrl *gomock.Controller) *MockCalculatorer {
+	mock := &MockCalculatorer{ctrl: ctrl}
+	mock.recorder = &MockCalculatorerMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use.
+func (m *MockCalculatorer) EXPECT() *MockCalculatorerMockRecorder {
+	return m.recorder
+}
+
+// Add mocks base method.
+func (m *MockCalculatorer) Add(arg0, arg1 int) int {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Add", arg0, arg1)
+	ret0, _ := ret[0].(int)
+	return ret0
+}
+
+// Add indicates an expected call of Add.
+func (mr *MockCalculatorerMockRecorder) Add(arg0, arg1 any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Add", reflect.TypeOf((*MockCalculatorer)(nil).Add), arg0, arg1)
+}
+
+// Divide mocks base method.
+func (m *MockCalculatorer) Divide(arg0, arg1 int) int {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Divide", arg0, arg1)
+	ret0, _ := ret[0].(int)
+	return ret0
+}
+
+// Divide indicates an expected call of Divide.
+func (mr *MockCalculatorerMockRecorder) Divide(arg0, arg1 any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Divide", reflect.TypeOf((*MockCalculatorer)(nil).Divide), arg0, arg1)
+}
+
+// Multiply mocks base method.
+func (m *MockCalculatorer) Multiply(arg0, arg1 int) int {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Multiply", arg0, arg1)
+	ret0, _ := ret[0].(int)
+	return ret0
+}
+
+// Multiply indicates an expected call of Multiply.
+func (mr *MockCalculatorerMockRecorder) Multiply(arg0, arg1 any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Multiply", reflect.TypeOf((*MockCalculatorer)(nil).Multiply), arg0, arg1)
+}
+
+// Subtract mocks base method.
+func (m *MockCalculatorer) Subtract(arg0, arg1 int) int {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Subtract", arg0, arg1)
+	ret0, _ := ret[0].(int)
+	return ret0
+}
+
+// Subtract indicates an expected call of Subtract.
+func (mr *MockCalculatorerMockRecorder) Subtract(arg0, arg1 any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Subtract", reflect.TypeOf((*MockCalculatorer)(nil).Subtract), arg0, arg1)
+}