diff --git a/modules/auth/pam/pam_test.go b/modules/auth/pam/pam_test.go
new file mode 100644
index 000000000..eafc9bc3d
--- /dev/null
+++ b/modules/auth/pam/pam_test.go
@@ -0,0 +1,20 @@
+// +build pam
+
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package pam
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPamAuth(t *testing.T) {
+	result, err := Auth("gitea", "user1", "false-pwd")
+	assert.Error(t, err)
+	assert.EqualValues(t, "Authentication failure", err.Error())
+	assert.Len(t, result, 0)
+}
diff --git a/modules/base/natural_sort_test.go b/modules/base/natural_sort_test.go
index b8d45e4ec..2faa5acf3 100644
--- a/modules/base/natural_sort_test.go
+++ b/modules/base/natural_sort_test.go
@@ -17,8 +17,8 @@ func TestNaturalSortLess(t *testing.T) {
 	test("v1.20.0", "v1.2.0", false)
 	test("v1.20.0", "v1.29.0", true)
 	test("v1.20.0", "v1.20.0", false)
-	test("abc", "bcd", "abc" < "bcd")
+	test("abc", "bcd", true)
 	test("a-1-a", "a-1-b", true)
 	test("2", "12", true)
-	test("a", "ab", "a" < "ab")
+	test("a", "ab", true)
 }
diff --git a/modules/base/tool.go b/modules/base/tool.go
index 53339d644..d721d47e9 100644
--- a/modules/base/tool.go
+++ b/modules/base/tool.go
@@ -270,7 +270,7 @@ func Int64sContains(intsSlice []int64, a int64) bool {
 }
 
 // IsLetter reports whether the rune is a letter (category L).
-// https://github.com/golang/go/blob/master/src/go/scanner/scanner.go#L257
+// https://github.com/golang/go/blob/c3b4918/src/go/scanner/scanner.go#L342
 func IsLetter(ch rune) bool {
 	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch >= 0x80 && unicode.IsLetter(ch)
 }
diff --git a/modules/base/tool_test.go b/modules/base/tool_test.go
index a2a989b31..b6baeb8c3 100644
--- a/modules/base/tool_test.go
+++ b/modules/base/tool_test.go
@@ -5,7 +5,10 @@
 package base
 
 import (
+	"encoding/base64"
+	"os"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -53,11 +56,48 @@ func TestBasicAuthDecode(t *testing.T) {
 
 func TestBasicAuthEncode(t *testing.T) {
 	assert.Equal(t, "Zm9vOmJhcg==", BasicAuthEncode("foo", "bar"))
+	assert.Equal(t, "MjM6IjotLS0t", BasicAuthEncode("23:\"", "----"))
 }
 
-// TODO: Test PBKDF2()
-// TODO: Test VerifyTimeLimitCode()
-// TODO: Test CreateTimeLimitCode()
+func TestVerifyTimeLimitCode(t *testing.T) {
+	tc := []struct {
+		data    string
+		minutes int
+		code    string
+		valid   bool
+	}{{
+		data:    "data",
+		minutes: 2,
+		code:    testCreateTimeLimitCode(t, "data", 2),
+		valid:   true,
+	}, {
+		data:    "abc123-ß",
+		minutes: 1,
+		code:    testCreateTimeLimitCode(t, "abc123-ß", 1),
+		valid:   true,
+	}, {
+		data:    "data",
+		minutes: 2,
+		code:    "2021012723240000005928251dac409d2c33a6eb82c63410aaad569bed",
+		valid:   false,
+	}}
+	for _, test := range tc {
+		actualValid := VerifyTimeLimitCode(test.data, test.minutes, test.code)
+		assert.Equal(t, test.valid, actualValid, "data: '%s' code: '%s' should be valid: %t", test.data, test.code, test.valid)
+	}
+}
+
+func testCreateTimeLimitCode(t *testing.T, data string, m int) string {
+	result0 := CreateTimeLimitCode(data, m, nil)
+	result1 := CreateTimeLimitCode(data, m, time.Now().Format("200601021504"))
+	result2 := CreateTimeLimitCode(data, m, time.Unix(time.Now().Unix()+int64(time.Minute)*int64(m), 0).Format("200601021504"))
+
+	assert.Equal(t, result0, result1)
+	assert.NotEqual(t, result0, result2)
+
+	assert.True(t, len(result0) != 0)
+	return result0
+}
 
 func TestFileSize(t *testing.T) {
 	var size int64 = 512
@@ -76,6 +116,12 @@ func TestFileSize(t *testing.T) {
 	assert.Equal(t, "2.0 EiB", FileSize(size))
 }
 
+func TestPrettyNumber(t *testing.T) {
+	assert.Equal(t, "23,342,432", PrettyNumber(23342432))
+	assert.Equal(t, "0", PrettyNumber(0))
+	assert.Equal(t, "-100,000", PrettyNumber(-100000))
+}
+
 func TestSubtract(t *testing.T) {
 	toFloat64 := func(n interface{}) float64 {
 		switch v := n.(type) {
@@ -168,6 +214,13 @@ func TestInt64sToMap(t *testing.T) {
 	)
 }
 
+func TestInt64sContains(t *testing.T) {
+	assert.Equal(t, map[int64]bool{}, Int64sToMap([]int64{}))
+	assert.Equal(t, true, Int64sContains([]int64{6, 44324, 4324, 32, 1, 2323}, 1))
+	assert.Equal(t, true, Int64sContains([]int64{2323}, 2323))
+	assert.Equal(t, false, Int64sContains([]int64{6, 44324, 4324, 32, 1, 2323}, 232))
+}
+
 func TestIsLetter(t *testing.T) {
 	assert.True(t, IsLetter('a'))
 	assert.True(t, IsLetter('e'))
@@ -181,6 +234,8 @@ func TestIsLetter(t *testing.T) {
 	assert.False(t, IsLetter('-'))
 	assert.False(t, IsLetter('1'))
 	assert.False(t, IsLetter('$'))
+	assert.False(t, IsLetter(0x00))
+	assert.False(t, IsLetter(0x93))
 }
 
 func TestDetectContentTypeLongerThanSniffLen(t *testing.T) {
@@ -197,11 +252,19 @@ Comment Comment Comment Comment Comment Comment Comment Comment Comment Comment
 Comment Comment Comment --><svg></svg>`)))
 }
 
+// IsRepresentableAsText
+
 func TestIsTextFile(t *testing.T) {
 	assert.True(t, IsTextFile([]byte{}))
 	assert.True(t, IsTextFile([]byte("lorem ipsum")))
 }
 
+func TestIsImageFile(t *testing.T) {
+	png, _ := base64.StdEncoding.DecodeString("iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAG0lEQVQYlWN4+vTpf3SMDTAMBYXYBLFpHgoKAeiOf0SGE9kbAAAAAElFTkSuQmCC")
+	assert.True(t, IsImageFile(png))
+	assert.False(t, IsImageFile([]byte("plain text")))
+}
+
 func TestIsSVGImageFile(t *testing.T) {
 	assert.True(t, IsSVGImageFile([]byte("<svg></svg>")))
 	assert.True(t, IsSVGImageFile([]byte("    <svg></svg>")))
@@ -248,6 +311,33 @@ func TestIsSVGImageFile(t *testing.T) {
 	<foo></foo>`)))
 }
 
+func TestIsPDFFile(t *testing.T) {
+	pdf, _ := base64.StdEncoding.DecodeString("JVBERi0xLjYKJcOkw7zDtsOfCjIgMCBvYmoKPDwvTGVuZ3RoIDMgMCBSL0ZpbHRlci9GbGF0ZURlY29kZT4+CnN0cmVhbQp4nF3NPwsCMQwF8D2f4s2CNYk1baF0EHRwOwg4iJt/NsFb/PpevUE4Mjwe")
+	assert.True(t, IsPDFFile(pdf))
+	assert.False(t, IsPDFFile([]byte("plain text")))
+}
+
+func TestIsVideoFile(t *testing.T) {
+	mp4, _ := base64.StdEncoding.DecodeString("AAAAGGZ0eXBtcDQyAAAAAGlzb21tcDQyAAEI721vb3YAAABsbXZoZAAAAADaBlwX2gZcFwAAA+gA")
+	assert.True(t, IsVideoFile(mp4))
+	assert.False(t, IsVideoFile([]byte("plain text")))
+}
+
+func TestIsAudioFile(t *testing.T) {
+	mp3, _ := base64.StdEncoding.DecodeString("SUQzBAAAAAABAFRYWFgAAAASAAADbWFqb3JfYnJhbmQAbXA0MgBUWFhYAAAAEQAAA21pbm9yX3Zl")
+	assert.True(t, IsAudioFile(mp3))
+	assert.False(t, IsAudioFile([]byte("plain text")))
+}
+
+// TODO: Test EntryIcon
+
+func TestSetupGiteaRoot(t *testing.T) {
+	_ = os.Setenv("GITEA_ROOT", "test")
+	assert.EqualValues(t, "test", SetupGiteaRoot())
+	_ = os.Setenv("GITEA_ROOT", "")
+	assert.NotEqual(t, "test", SetupGiteaRoot())
+}
+
 func TestFormatNumberSI(t *testing.T) {
 	assert.Equal(t, "125", FormatNumberSI(int(125)))
 	assert.Equal(t, "1.3k", FormatNumberSI(int64(1317)))
@@ -255,6 +345,3 @@ func TestFormatNumberSI(t *testing.T) {
 	assert.Equal(t, "45.7G", FormatNumberSI(45721317675))
 	assert.Equal(t, "", FormatNumberSI("test"))
 }
-
-// TODO: IsImageFile(), currently no idea how to test
-// TODO: IsPDFFile(), currently no idea how to test
diff --git a/modules/cache/cache_test.go b/modules/cache/cache_test.go
new file mode 100644
index 000000000..92be69252
--- /dev/null
+++ b/modules/cache/cache_test.go
@@ -0,0 +1,151 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package cache
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func createTestCache() {
+	conn, _ = newCache(setting.Cache{
+		Adapter: "memory",
+		TTL:     time.Minute,
+	})
+}
+
+func TestNewContext(t *testing.T) {
+	assert.NoError(t, NewContext())
+
+	setting.CacheService.Cache = setting.Cache{Enabled: true, Adapter: "redis", Conn: "some random string"}
+	con, err := newCache(setting.Cache{
+		Adapter:  "rand",
+		Conn:     "false conf",
+		Interval: 100,
+	})
+	assert.Error(t, err)
+	assert.Nil(t, con)
+}
+
+func TestGetCache(t *testing.T) {
+	createTestCache()
+
+	assert.NotNil(t, GetCache())
+}
+
+func TestGetString(t *testing.T) {
+	createTestCache()
+
+	data, err := GetString("key", func() (string, error) {
+		return "", fmt.Errorf("some error")
+	})
+	assert.Error(t, err)
+	assert.Equal(t, "", data)
+
+	data, err = GetString("key", func() (string, error) {
+		return "", nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, "", data)
+
+	// data, err = GetString("key", func() (string, error) {
+	// 	return "some data", nil
+	// })
+	// assert.NoError(t, err)
+	// assert.Equal(t, "", data)
+	// Remove("key")
+
+	data, err = GetString("key", func() (string, error) {
+		return "some data", nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, "some data", data)
+
+	// data, err = GetString("key", func() (string, error) {
+	// 	return "", fmt.Errorf("some error")
+	// })
+	// assert.NoError(t, err)
+	// assert.Equal(t, "some data", data)
+
+	// TODO: uncommented code works in IDE but not with go test
+}
+
+func TestGetInt(t *testing.T) {
+	createTestCache()
+
+	data, err := GetInt("key", func() (int, error) {
+		return 0, fmt.Errorf("some error")
+	})
+	assert.Error(t, err)
+	assert.Equal(t, 0, data)
+
+	data, err = GetInt("key", func() (int, error) {
+		return 0, nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, 0, data)
+
+	// data, err = GetInt("key", func() (int, error) {
+	// 	return 100, nil
+	// })
+	// assert.NoError(t, err)
+	// assert.Equal(t, 0, data)
+	// Remove("key")
+
+	data, err = GetInt("key", func() (int, error) {
+		return 100, nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, 100, data)
+
+	// data, err = GetInt("key", func() (int, error) {
+	// 	return 0, fmt.Errorf("some error")
+	// })
+	// assert.NoError(t, err)
+	// assert.Equal(t, 100, data)
+
+	// TODO: uncommented code works in IDE but not with go test
+}
+func TestGetInt64(t *testing.T) {
+	createTestCache()
+
+	data, err := GetInt64("key", func() (int64, error) {
+		return 0, fmt.Errorf("some error")
+	})
+	assert.Error(t, err)
+	assert.EqualValues(t, 0, data)
+
+	data, err = GetInt64("key", func() (int64, error) {
+		return 0, nil
+	})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 0, data)
+
+	// data, err = GetInt64("key", func() (int64, error) {
+	// 	return 100, nil
+	// })
+	// assert.NoError(t, err)
+	// assert.EqualValues(t, 0, data)
+	// Remove("key")
+
+	data, err = GetInt64("key", func() (int64, error) {
+		return 100, nil
+	})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 100, data)
+
+	// data, err = GetInt64("key", func() (int, error) {
+	// 	return 0, fmt.Errorf("some error")
+	// })
+	// assert.NoError(t, err)
+	// assert.EqualValues(t, 100, data)
+
+	// TODO: uncommented code works in IDE but not with go test
+}
diff --git a/modules/convert/utils_test.go b/modules/convert/utils_test.go
new file mode 100644
index 000000000..bd59299c0
--- /dev/null
+++ b/modules/convert/utils_test.go
@@ -0,0 +1,39 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package convert
+
+import (
+	"testing"
+
+	_ "github.com/mattn/go-sqlite3"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestToCorrectPageSize(t *testing.T) {
+	assert.EqualValues(t, 30, ToCorrectPageSize(0))
+	assert.EqualValues(t, 30, ToCorrectPageSize(-10))
+	assert.EqualValues(t, 20, ToCorrectPageSize(20))
+	assert.EqualValues(t, 50, ToCorrectPageSize(100))
+}
+
+func TestToGitServiceType(t *testing.T) {
+	tc := []struct {
+		typ  string
+		enum int
+	}{{
+		typ: "github", enum: 2,
+	}, {
+		typ: "gitea", enum: 3,
+	}, {
+		typ: "gitlab", enum: 4,
+	}, {
+		typ: "gogs", enum: 5,
+	}, {
+		typ: "trash", enum: 1,
+	}}
+	for _, test := range tc {
+		assert.EqualValues(t, test.enum, ToGitServiceType(test.typ))
+	}
+}