diff --git a/helper_test.go b/helper_test.go
new file mode 100644
index 0000000..c7e65eb
--- /dev/null
+++ b/helper_test.go
@@ -0,0 +1,8 @@
+package main
+
+import "go.uber.org/zap"
+
+// NextVersion is a test fixture to expose the private nextVersion() function.
+func NextVersion(log *zap.Logger, path string) (string, error) {
+	return nextVersion(log, path)
+}
diff --git a/main_test.go b/main_test.go
new file mode 100644
index 0000000..5a3a163
--- /dev/null
+++ b/main_test.go
@@ -0,0 +1,75 @@
+package main_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os/exec"
+	"testing"
+
+	ccv "github.com/smlx/ccv"
+	"go.uber.org/zap"
+)
+
+func TestNextVersion(t *testing.T) {
+	var testCases = map[string]struct {
+		gitCmds [][]string
+		expect  string
+	}{
+		"none": {gitCmds: [][]string{
+			{"commit", "--allow-empty", "-m", "feat: initial commit"},
+			{"tag", "v0.1.0"},
+			{"commit", "--allow-empty", "-m", "chore: not much"},
+		}, expect: "v0.1.0"},
+		"patch": {gitCmds: [][]string{
+			{"commit", "--allow-empty", "-m", "feat: initial commit"},
+			{"tag", "v0.1.0"},
+			{"commit", "--allow-empty", "-m", "fix: minor bug"},
+		}, expect: "v0.1.1"},
+		"minor": {gitCmds: [][]string{
+			{"commit", "--allow-empty", "-m", "feat: initial commit"},
+			{"tag", "v0.1.0"},
+			{"commit", "--allow-empty", "-m", "feat: cool new feature"},
+		}, expect: "v0.2.0"},
+		"major": {gitCmds: [][]string{
+			{"commit", "--allow-empty", "-m", "feat: initial commit"},
+			{"tag", "v0.1.0"},
+			{"commit", "--allow-empty", "-m", "feat: major refactor\nBREAKING CHANGE: new stuff"},
+		}, expect: "v1.0.0"},
+	}
+	log, err := zap.NewDevelopment()
+	if err != nil {
+		t.Fatalf("couldn't get logger: %v", err)
+	}
+	for name, tc := range testCases {
+		t.Run(name, func(tt *testing.T) {
+			// create test dir
+			dir, err := ioutil.TempDir("", "example")
+			if err != nil {
+				tt.Fatalf("couldn't get a tempdir: %v", err)
+			}
+			// init git repo
+			initCmd := exec.Command("git", "init")
+			initCmd.Dir = dir
+			initCmd.Env = []string{fmt.Sprintf("HOME=%s", dir)}
+			if err = initCmd.Run(); err != nil {
+				tt.Fatalf("couldn't git init: %v", err)
+			}
+			for _, c := range tc.gitCmds {
+				cmd := exec.Command("git", c...)
+				cmd.Dir = dir
+				cmd.Env = []string{fmt.Sprintf("HOME=%s", dir)}
+				if err = cmd.Run(); err != nil {
+					tt.Fatalf("couldn't run git command `%s`: %v", c, err)
+				}
+			}
+			tt.Log(dir)
+			next, err := ccv.NextVersion(log, dir)
+			if err != nil {
+				tt.Fatalf("error from main.nextVersion(): %v", err)
+			}
+			if next != tc.expect {
+				tt.Fatalf("expected: %v, got: %v", tc.expect, next)
+			}
+		})
+	}
+}