[#85] Add integration tests

Signed-off-by: Denis Kirillov <denis@nspcc.ru>

downloader/reader_test.go

@@ -1,8 +1,10 @@
 package downloader
 
 import (
+	"bytes"
 	"fmt"
 	"io"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -41,3 +43,44 @@ func TestReader(t *testing.T) {
 		require.Equal(t, data, res)
 	}
 }
+
+func TestDetector(t *testing.T) {
+	txtContentType := "text/plain; charset=utf-8"
+	sb := strings.Builder{}
+	for i := 0; i < 10; i++ {
+		sb.WriteString("Some txt content. Content-Type must be detected properly by detector.")
+	}
+
+	for _, tc := range []struct {
+		Name        string
+		ContentType string
+		Expected    string
+	}{
+		{
+			Name:        "less than 512b",
+			ContentType: txtContentType,
+			Expected:    sb.String()[:256],
+		},
+		{
+			Name:        "more than 512b",
+			ContentType: txtContentType,
+			Expected:    sb.String(),
+		},
+	} {
+		t.Run(tc.Name, func(t *testing.T) {
+			detector := newDetector()
+
+			go func() {
+				detector.SetReader(bytes.NewBufferString(tc.Expected))
+				detector.Detect()
+			}()
+
+			detector.Wait()
+			require.Equal(t, tc.ContentType, detector.contentType)
+
+			data, err := io.ReadAll(detector.MultiReader())
+			require.NoError(t, err)
+			require.Equal(t, tc.Expected, string(data))
+		})
+	}
+}