diff --git a/go.mod b/go.mod
index d6fb5c7..4eece65 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,7 @@ module kubemodcmp
 go 1.22.1
 
 require (
+	github.com/rogpeppe/go-internal v1.12.0
 	github.com/urfave/cli v1.22.14
 	golang.org/x/mod v0.17.0
 )
@@ -10,4 +11,6 @@ require (
 require (
 	github.com/cpuguy83/go-md2man/v2 v2.0.2 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
+	golang.org/x/sys v0.12.0 // indirect
+	golang.org/x/tools v0.13.0 // indirect
 )
diff --git a/go.sum b/go.sum
index b3d9c1c..e4f76f6 100644
--- a/go.sum
+++ b/go.sum
@@ -6,6 +6,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rogpeppe/go-internal v1.12.0 h1:exVL4IDcn6na9z1rAb56Vxr+CgyK3nn3O+epU5NdKM8=
+github.com/rogpeppe/go-internal v1.12.0/go.mod h1:E+RYuTGaKKdloAfM02xzb0FW3Paa99yedzYV+kq4uf4=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -19,6 +21,10 @@ github.com/urfave/cli v1.22.14 h1:ebbhrRiGK2i4naQJr+1Xj92HXZCrK7MsyTS/ob3HnAk=
 github.com/urfave/cli v1.22.14/go.mod h1:X0eDS6pD6Exaclxm99NJ3FiCDRED7vIHpx2mDOHLvkA=
 golang.org/x/mod v0.17.0 h1:zY54UmvipHiNd+pm+m0x9KhZ9hl1/7QNMyxXbc6ICqA=
 golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/sys v0.12.0 h1:CM0HF96J0hcLAwsHPJZjfdNzs0gftsLfgKt57wWHJ0o=
+golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/tools v0.13.0 h1:Iey4qkscZuv0VvIt8E0neZjtPVQFSc870HQ448QgEmQ=
+golang.org/x/tools v0.13.0/go.mod h1:HvlwmtVNQAhOuCjW7xxvovg8wbNq7LwfXh/k7wXUl58=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/main.go b/main.go
index 8be5e50..8f1f3b3 100644
--- a/main.go
+++ b/main.go
@@ -352,6 +352,8 @@ func checkCmd() cli.Command {
 					if err = runGo(ctx.Args().First(), "mod", "edit", fmt.Sprintf("-go=%s", k8s.GoVersion)); err != nil {
 						return fmt.Errorf("fixing Go version: %w", err)
 					}
+				} else {
+					return fmt.Errorf("wrong Go version: %w", err)
 				}
 			}
 
diff --git a/main_test.go b/main_test.go
new file mode 100644
index 0000000..e681ed9
--- /dev/null
+++ b/main_test.go
@@ -0,0 +1,51 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/rogpeppe/go-internal/testscript"
+)
+
+func TestMain(m *testing.M) {
+	os.Exit(testscript.RunMain(m, map[string]func() int{
+		"kubemodcmp": func() (exitCode int) {
+			defer func() {
+				if val := recover(); val != nil {
+					exitCode = recover().(int)
+				}
+			}()
+			main()
+			return 0
+		},
+	}))
+}
+
+func TestScript(t *testing.T) {
+	testscript.Run(t, testscript.Params{
+		Dir:      "testdata",
+		TestWork: true,
+		Setup: func(env *testscript.Env) error {
+			path := os.Getenv("GOPATH")
+			if os.Getenv("GOPATH") == "" {
+				path = filepath.Join(env.WorkDir, ".go")
+			}
+			env.Setenv("GOPATH", path)
+
+			if os.Getenv("GOCACHE") != "" {
+				env.Setenv("GOCACHE", os.Getenv("GOCACHE"))
+			} else {
+				env.Setenv("GOCACHE", filepath.Join(path, "cache"))
+			}
+
+			// TODO: Use global cache instead of one per txtar
+			if os.Getenv("GOMODCACHE") != "" {
+				env.Setenv("GOMODCACHE", os.Getenv("GOMODCACHE"))
+			} else {
+				env.Setenv("GOMODCACHE", filepath.Join(path, "modcache"))
+			}
+			return nil
+		},
+	})
+}
diff --git a/testdata/check-dep-need-downgrade.txt b/testdata/check-dep-need-downgrade.txt
new file mode 100644
index 0000000..f491fda
--- /dev/null
+++ b/testdata/check-dep-need-downgrade.txt
@@ -0,0 +1,41 @@
+exec go mod tidy
+! kubemodcmp check .
+stderr 'golang.org/x/net'
+
+kubemodcmp check --fix .
+kubemodcmp check .
+! stderr .
+
+-- go.mod --
+module foo
+
+go 1.20
+
+toolchain go1.22.2
+
+require k8s.io/apimachinery v0.28.6
+
+require (
+	github.com/go-logr/logr v1.2.4 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/google/gofuzz v1.2.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	golang.org/x/net v0.20.0 // indirect
+	golang.org/x/text v0.14.0 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	k8s.io/klog/v2 v2.100.1 // indirect
+	k8s.io/utils v0.0.0-20230406110748-d93618cff8a2 // indirect
+	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd // indirect
+	sigs.k8s.io/structured-merge-diff/v4 v4.2.3 // indirect
+)
+-- main.go --
+package main
+
+import metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+var _ any = metav1.TypeMeta{}
+
+func main() {}
diff --git a/testdata/check-go-need-downgrade.txt b/testdata/check-go-need-downgrade.txt
new file mode 100644
index 0000000..bb20e66
--- /dev/null
+++ b/testdata/check-go-need-downgrade.txt
@@ -0,0 +1,39 @@
+exec go mod tidy
+! kubemodcmp check .
+stderr .
+
+kubemodcmp check --fix .
+kubemodcmp check .
+! stderr .
+
+-- go.mod --
+module foo
+
+go 1.22
+
+require k8s.io/apimachinery v0.28.6
+
+require (
+	github.com/go-logr/logr v1.2.4 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/google/gofuzz v1.2.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	golang.org/x/net v0.19.0 // indirect
+	golang.org/x/text v0.14.0 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	k8s.io/klog/v2 v2.100.1 // indirect
+	k8s.io/utils v0.0.0-20230406110748-d93618cff8a2 // indirect
+	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd // indirect
+	sigs.k8s.io/structured-merge-diff/v4 v4.2.3 // indirect
+)
+-- main.go --
+package main
+
+import metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+var _ any = metav1.TypeMeta{}
+
+func main() {}
diff --git a/testdata/check-go-need-upgrade.txt b/testdata/check-go-need-upgrade.txt
new file mode 100644
index 0000000..06938a8
--- /dev/null
+++ b/testdata/check-go-need-upgrade.txt
@@ -0,0 +1,39 @@
+exec go mod tidy
+! kubemodcmp check .
+stderr .
+
+kubemodcmp check --fix .
+kubemodcmp check .
+! stderr .
+
+-- go.mod --
+module foo
+
+go 1.19
+
+require k8s.io/apimachinery v0.28.6
+
+require (
+	github.com/go-logr/logr v1.2.4 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/google/gofuzz v1.2.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	golang.org/x/net v0.19.0 // indirect
+	golang.org/x/text v0.14.0 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	k8s.io/klog/v2 v2.100.1 // indirect
+	k8s.io/utils v0.0.0-20230406110748-d93618cff8a2 // indirect
+	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd // indirect
+	sigs.k8s.io/structured-merge-diff/v4 v4.2.3 // indirect
+)
+-- main.go --
+package main
+
+import metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+var _ any = metav1.TypeMeta{}
+
+func main() {}
diff --git a/testdata/check-ignore-absent-deps.txt b/testdata/check-ignore-absent-deps.txt
new file mode 100644
index 0000000..65f5e5e
--- /dev/null
+++ b/testdata/check-ignore-absent-deps.txt
@@ -0,0 +1,62 @@
+exec go mod tidy
+
+# golang.org/x/sys is not inside the go.mod file, but it ends up in the
+# dependencies via `go list -m all`. Since it's not part of the go.mod file,
+# the check command shouldn't trip on it.
+
+exec cat go.mod
+! stdout `golang.org/x/sync`
+
+exec go list -m all
+# That version of kubernetes imports golang.org/x/sync v0.5.0, but 
+stdout 'golang.org/x/sync v0.2.0'
+
+kubemodcmp check .
+! stderr .
+
+-- go.mod --
+module foo
+
+go 1.20
+
+require (
+	github.com/prometheus/client_golang v1.16.0
+	k8s.io/apimachinery v0.28.6
+)
+
+require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.2.0 // indirect
+	github.com/go-logr/logr v1.2.4 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/golang/protobuf v1.5.3 // indirect
+	github.com/google/gofuzz v1.2.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/kr/text v0.2.0 // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.4 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/prometheus/client_model v0.4.0 // indirect
+	github.com/prometheus/common v0.44.0 // indirect
+	github.com/prometheus/procfs v0.10.1 // indirect
+	golang.org/x/net v0.19.0 // indirect
+	golang.org/x/sys v0.15.0 // indirect
+	golang.org/x/text v0.14.0 // indirect
+	google.golang.org/protobuf v1.31.0 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	k8s.io/klog/v2 v2.100.1 // indirect
+	k8s.io/utils v0.0.0-20230406110748-d93618cff8a2 // indirect
+	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd // indirect
+	sigs.k8s.io/structured-merge-diff/v4 v4.2.3 // indirect
+)
+-- main.go --
+package main
+
+import metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+import "github.com/prometheus/client_golang/prometheus"
+
+var _ any = metav1.TypeMeta{}
+var _ any = prometheus.DescribeByCollect
+
+func main() {}
diff --git a/testdata/check-success.txt b/testdata/check-success.txt
new file mode 100644
index 0000000..35729fd
--- /dev/null
+++ b/testdata/check-success.txt
@@ -0,0 +1,34 @@
+exec go mod tidy
+kubemodcmp check .
+
+-- go.mod --
+module foo
+
+go 1.20
+
+require k8s.io/apimachinery v0.28.6
+
+require (
+	github.com/go-logr/logr v1.2.4 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/google/gofuzz v1.2.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	golang.org/x/net v0.19.0 // indirect
+	golang.org/x/text v0.14.0 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	k8s.io/klog/v2 v2.100.1 // indirect
+	k8s.io/utils v0.0.0-20230406110748-d93618cff8a2 // indirect
+	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd // indirect
+	sigs.k8s.io/structured-merge-diff/v4 v4.2.3 // indirect
+)
+-- main.go --
+package main
+
+import metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+var _ any = metav1.TypeMeta{}
+
+func main() {}