dockerversion: add a basic unit-test

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit eb9a5392bcbcf140bfd29c9ec2ba29e7100a27a4)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

dockerversion/useragent_test.go

@@ -0,0 +1,24 @@
+package dockerversion
+
+import (
+	"context"
+	"testing"
+
+	"gotest.tools/v3/assert"
+	is "gotest.tools/v3/assert/cmp"
+)
+
+func TestDockerUserAgent(t *testing.T) {
+	t.Run("daemon user-agent", func(t *testing.T) {
+		ua := DockerUserAgent(context.TODO())
+		expected := getDaemonUserAgent()
+		assert.Check(t, is.Equal(ua, expected))
+	})
+
+	t.Run("daemon user-agent with upstream", func(t *testing.T) {
+		ctx := context.WithValue(context.TODO(), UAStringKey{}, "Magic-Client/1.2.3 (linux)")
+		ua := DockerUserAgent(ctx)
+		expected := getDaemonUserAgent() + ` UpstreamClient(Magic-Client/1.2.3 \(linux\))`
+		assert.Check(t, is.Equal(ua, expected))
+	})
+}