diff --git a/exports_test.go b/exports_test.go
index 5b0d4377..dc00dd40 100644
--- a/exports_test.go
+++ b/exports_test.go
@@ -4,7 +4,6 @@ import (
 	"context"
 	"testing"
 
-	"github.com/facebookgo/ensure"
 	"github.com/mailgun/mailgun-go/v4"
 	"github.com/stretchr/testify/require"
 )
@@ -43,5 +42,5 @@ func TestExportsLink(t *testing.T) {
 	ctx := context.Background()
 	url, err := mg.GetExportLink(ctx, "12")
 	require.NoError(t, err)
-	ensure.StringContains(t, url, "/some/s3/url")
+	require.Contains(t, url, "/some/s3/url")
 }
diff --git a/messages_test.go b/messages_test.go
index 1a0ccf85..816f82aa 100644
--- a/messages_test.go
+++ b/messages_test.go
@@ -11,7 +11,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/facebookgo/ensure"
 	"github.com/mailgun/mailgun-go/v4"
 	"github.com/stretchr/testify/require"
 )
@@ -492,8 +491,9 @@ func TestSendEOFError(t *testing.T) {
 	m := mailgun.NewMessage(fromUser, exampleSubject, exampleText, toUser)
 	_, _, err := mg.Send(context.Background(), m)
 	require.NotNil(t, err)
-	ensure.StringContains(t, err.Error(), "remote server prematurely closed connection: Post ")
-	ensure.StringContains(t, err.Error(), "EOF")
+	// TODO(vtopc): do not compare strings, use errors.Is or errors.As:
+	require.Contains(t, err.Error(), "remote server prematurely closed connection: Post ")
+	require.ErrorIs(t, err, io.EOF)
 }
 
 func TestHasRecipient(t *testing.T) {
@@ -596,7 +596,7 @@ func TestAddOverrideHeader(t *testing.T) {
 	require.Equal(t, exampleMessage, msg)
 	require.Equal(t, exampleID, id)
 
-	ensure.StringContains(t, mg.GetCurlOutput(), "Host:")
+	require.Contains(t, mg.GetCurlOutput(), "Host:")
 }
 
 func TestOnBehalfOfSubaccount(t *testing.T) {
@@ -635,7 +635,7 @@ func TestOnBehalfOfSubaccount(t *testing.T) {
 	require.Equal(t, exampleMessage, msg)
 	require.Equal(t, exampleID, id)
 
-	ensure.StringContains(t, mg.GetCurlOutput(), "Host:")
+	require.Contains(t, mg.GetCurlOutput(), "Host:")
 }
 
 func TestCaptureCurlOutput(t *testing.T) {
@@ -664,7 +664,7 @@ func TestCaptureCurlOutput(t *testing.T) {
 	require.Equal(t, exampleMessage, msg)
 	require.Equal(t, exampleID, id)
 
-	ensure.StringContains(t, mg.GetCurlOutput(), "curl")
+	require.Contains(t, mg.GetCurlOutput(), "curl")
 	t.Logf("%s", mg.GetCurlOutput())
 }
 
diff --git a/parse_test.go b/parse_test.go
index 41878517..c857854f 100644
--- a/parse_test.go
+++ b/parse_test.go
@@ -6,14 +6,15 @@ import (
 	"testing"
 	"time"
 
-	"github.com/facebookgo/ensure"
 	"github.com/mailgun/mailgun-go/v4/events"
 	"github.com/stretchr/testify/require"
 )
 
 func TestParseErrors(t *testing.T) {
 	_, err := ParseEvent([]byte(""))
-	ensure.StringContains(t, err.Error(), "failed to recognize event")
+	require.NotNil(t, err)
+	// TODO(vtopc): do not compare strings, use errors.Is or errors.As:
+	require.Contains(t, err.Error(), "failed to recognize event")
 
 	_, err = ParseEvent([]byte(`{"event": "unknown_event"}`))
 	require.EqualError(t, err, "unsupported event: 'unknown_event'")
@@ -22,7 +23,8 @@ func TestParseErrors(t *testing.T) {
 		"event": "accepted",
 		"timestamp": "1420255392.850187"
 	}`))
-	ensure.StringContains(t, err.Error(), "failed to parse event 'accepted'")
+	// TODO(vtopc): do not compare strings, use errors.Is or errors.As:
+	require.Contains(t, err.Error(), "failed to parse event 'accepted'")
 }
 
 func TestParseSuccess(t *testing.T) {