From bc55118b5bf0370d497933997cba77e575a0c4a9 Mon Sep 17 00:00:00 2001
From: Mengjiao Liu <mengjiao.liu@daocloud.io>
Date: Thu, 10 Feb 2022 18:48:07 +0800
Subject: [PATCH] Improve test coverage: add unit tests `TestReadAtMost` in
 `pkg/util/tail`

---
 pkg/util/tail/tail_test.go | 69 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/pkg/util/tail/tail_test.go b/pkg/util/tail/tail_test.go
index 18d3f90c21a..641cfb10209 100644
--- a/pkg/util/tail/tail_test.go
+++ b/pkg/util/tail/tail_test.go
@@ -18,10 +18,79 @@ package tail
 
 import (
 	"bytes"
+	"io/ioutil"
+	"os"
 	"strings"
 	"testing"
 )
 
+func TestReadAtMost(t *testing.T) {
+	file, err := ioutil.TempFile("", "TestFileReadAtMost")
+	if err != nil {
+		t.Fatalf("unable to create temp file")
+	}
+	defer os.Remove(file.Name())
+
+	line := strings.Repeat("a", blockSize)
+	testBytes := []byte(line + "\n" +
+		line + "\n" +
+		line + "\n" +
+		line + "\n" +
+		line[blockSize/2:]) // incomplete line
+
+	file.Write(testBytes)
+	testCases := []struct {
+		name          string
+		max           int64
+		longerThanMax bool
+		expected      string
+	}{
+		{
+			name:          "the max is negative",
+			max:           -1,
+			longerThanMax: true,
+			expected:      "",
+		},
+		{
+			name:          "the max is zero",
+			max:           0,
+			longerThanMax: true,
+			expected:      "",
+		},
+		{
+			name:          "the file length is longer than max",
+			max:           1,
+			longerThanMax: true,
+			expected:      "a",
+		},
+		{
+			name:          "the file length is longer than max and contains newlines",
+			max:           blockSize,
+			longerThanMax: true,
+			expected:      strings.Repeat("a", blockSize/2-1) + "\n" + strings.Repeat("a", blockSize/2),
+		},
+		{
+			name:          "the max is longer than file length ",
+			max:           4613,
+			longerThanMax: false,
+			expected:      string(testBytes),
+		},
+	}
+
+	for _, test := range testCases {
+		readAtMostBytes, longerThanMax, err := ReadAtMost(file.Name(), test.max)
+		if err != nil {
+			t.Fatalf("Unexpected failure %v", err)
+		}
+		if test.longerThanMax != longerThanMax {
+			t.Fatalf("Unexpected result on whether the file length longer than the max, want: %t, got: %t", test.longerThanMax, longerThanMax)
+		}
+		if test.expected != string(readAtMostBytes) {
+			t.Fatalf("Unexpected most max bytes, want: %s, got: %s", test.expected, readAtMostBytes)
+		}
+	}
+}
+
 func TestTail(t *testing.T) {
 	line := strings.Repeat("a", blockSize)
 	testBytes := []byte(line + "\n" +