Added unit tests.

.github/workflows/test.yml

@@ -0,0 +1,19 @@
+name: Test
+on: [push, pull_request]
+jobs:
+  build:
+    name: Test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Go 1.13
+        uses: actions/setup-go@v1
+        with:
+          go-version: 1.13
+        id: go
+
+      - uses: actions/checkout@v2
+
+      - name: Test
+        run: |
+          go get -d -v
+          go test

.gitignore

@@ -0,0 +1 @@
+out

README.md

@@ -1,8 +1,9 @@
 # Find and Replace Action
 
 [![GitHub Marketplace](https://img.shields.io/badge/Marketplace-Find%20and%20Replace-blue.svg?colorA=24292e&colorB=0366d6&style=flat&longCache=true&logo=data:image/png;base64,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)](https://github.com/jacobtomlinson/gha-find-replace)
-[![Actions Status](https://github.com/jacobtomlinson/gha-find-replace/workflows/Build/badge.svg)](https://github.com/jacobtomlinson/gha-find-replace/actions)
-[![Actions Status](https://github.com/jacobtomlinson/gha-find-replace/workflows/Integration%20Test/badge.svg)](https://github.com/jacobtomlinson/gha-find-replace/actions)
+[![Build](https://github.com/jacobtomlinson/gha-find-replace/workflows/Build/badge.svg)](https://github.com/jacobtomlinson/gha-find-replace/actions)
+[![Integration Tests](https://github.com/jacobtomlinson/gha-find-replace/workflows/Integration%20Test/badge.svg)](https://github.com/jacobtomlinson/gha-find-replace/actions)
+[![Unit Tests](https://github.com/jacobtomlinson/gha-find-replace/actions/workflows/test.yml/badge.svg)](https://github.com/jacobtomlinson/gha-find-replace/actions/workflows/test.yml)
 
 This action will find and replace strings in your project files.
 
@@ -159,6 +160,25 @@ _If you need the push event to trigger other workflows, use a `repo` scoped [Per
           branch: ${{ github.ref }}
 ```
 
+## Contributing
+
+Install [go](https://go.dev/doc/install). This project currently uses Go 1.13. We recommend [gvm](https://github.com/moovweb/gvm) to switch between multiple go versions.
+
+```
+$ go version
+go version go1.13 darwin/amd64
+```
+
+Build and test.
+
+```
+go get -d -v
+go test
+go build -v .
+```
+
+Make your code changes, add tests, and make a pull request!
+
 ## Publishing
 
 To publish a new version of this Action we need to update the Docker image tag in `action.yml` and also create a new release on GitHub.

main_test.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestHappyPath(t *testing.T) {
+	if err := ioutil.WriteFile("out/data.txt", []byte("Hello world\n"), 0644); err != nil {
+		t.Error(err)
+	}
+
+	os.Setenv("INPUT_INCLUDE", "out/data.txt")
+	os.Setenv("INPUT_EXCLUDE", "")
+	os.Setenv("INPUT_FIND", "world")
+	os.Setenv("INPUT_REPLACE", "there")
+	os.Setenv("GITHUB_OUTPUT", "out/output.txt")
+
+	main()
+
+	data, err := ioutil.ReadFile("out/data.txt")
+	if err != nil {
+		t.Error(err)
+	}
+
+	want := "Hello there\n"
+	if string(data) != want {
+		t.Errorf("got %q, wanted %q", data, want)
+	}
+}