feat: support providing a list of allowed packages

README.md

@@ -37,11 +37,15 @@ linters:
     testpackage
 ```
 
-You can also change regexp that is used to ignore files by the linter. Here is the default value.
+You can also change the regexp that is used to ignore files by the linter,
+and the list of packages that are allowed by default.
+
+Here are the default values:
 ```yaml
 linters-settings:
   testpackage:
     skip-regexp: (export|internal)_test\.go
+    allow-packages: main
 ```
 
 ### Run
@@ -79,6 +83,8 @@ Usage: testpackage [-flag] [package]
 Flags:
   -skip-regexp string
         regexp pattern to skip file by name. To not skip files use -skip-regexp="^$" (default "(export|internal)_test\\.go")
+  -allow-packages string
+        comma separated list of packages that don't end with _test that tests are allowed to be in
   -V    print version and exit
   -c int
         display offending line with this many lines of context (default -1)

pkg/testpackage/testdata/allowed/allowed.go

@@ -0,0 +1 @@
+package allowed

pkg/testpackage/testdata/allowed/allowed_internal_test.go

@@ -0,0 +1 @@
+package allowed

pkg/testpackage/testdata/allowed/allowed_test.go

@@ -0,0 +1 @@
+package allowed

pkg/testpackage/testdata/allowed/export_test.go

@@ -0,0 +1 @@
+package allowed

pkg/testpackage/testdata/allowed/internal_test.go

@@ -0,0 +1 @@
+package allowed

pkg/testpackage/testpackage.go

@@ -5,6 +5,8 @@ import (
 	"regexp"
 	"strings"
 
+	"go/ast"
+
 	"golang.org/x/tools/go/analysis"
 )
 
@@ -14,37 +16,55 @@ const (
 	SkipRegexpFlagDefault = `(export|internal)_test\.go`
 )
 
+const (
+	AllowPackagesFlagName    = "allow-packages"
+	AllowPackagesFlagUsage   = `comma separated list of packages that don't end with _test that tests are allowed to be in`
+	AllowPackagesFlagDefault = `main`
+)
+
+func processTestFile(pass *analysis.Pass, f *ast.File, allowedPackages []string) {
+	packageName := f.Name.Name
+
+	for _, p := range allowedPackages {
+		if p == packageName {
+			return
+		}
+	}
+
+	if !strings.HasSuffix(packageName, "_test") {
+		pass.Reportf(f.Name.Pos(), "package should be `%s_test` instead of `%s`", packageName, packageName)
+	}
+}
+
 // NewAnalyzer returns Analyzer that makes you use a separate _test package.
 func NewAnalyzer() *analysis.Analyzer {
 	var (
-		skipFileRegexp = SkipRegexpFlagDefault
-		fs             flag.FlagSet
+		skipFileRegexp   = SkipRegexpFlagDefault
+		allowPackagesStr = AllowPackagesFlagDefault
+		fs               flag.FlagSet
 	)
 
 	fs.StringVar(&skipFileRegexp, SkipRegexpFlagName, skipFileRegexp, SkipRegexpFlagUsage)
+	fs.StringVar(&allowPackagesStr, AllowPackagesFlagName, allowPackagesStr, AllowPackagesFlagUsage)
 
 	return &analysis.Analyzer{
 		Name:  "testpackage",
 		Doc:   "linter that makes you use a separate _test package",
 		Flags: fs,
 		Run: func(pass *analysis.Pass) (interface{}, error) {
+			allowedPackages := strings.Split(allowPackagesStr, ",")
 			skipFile, err := regexp.Compile(skipFileRegexp)
 			if err != nil {
 				return nil, err
 			}
 
 			for _, f := range pass.Files {
 				fileName := pass.Fset.Position(f.Pos()).Filename
-				if skipFile.MatchString(fileName) {
+				if !strings.HasSuffix(fileName, "_test.go") || skipFile.MatchString(fileName) {
 					continue
 				}
 
-				if strings.HasSuffix(fileName, "_test.go") {
-					packageName := f.Name.Name
-					if !strings.HasSuffix(packageName, "_test") {
-						pass.Reportf(f.Name.Pos(), "package should be `%s_test` instead of `%s`", packageName, packageName)
-					}
-				}
+				processTestFile(pass, f, allowedPackages)
 			}
 
 			return nil, nil

pkg/testpackage/testpackage_test.go

@@ -27,6 +27,22 @@ func TestAnalyzer_Bad(t *testing.T) {
 	analysistest.Run(t, testdata, testpackage.NewAnalyzer())
 }
 
+func TestAnalyzer_Allowed(t *testing.T) {
+	analyzer := testpackage.NewAnalyzer()
+	err := analyzer.Flags.Set(testpackage.AllowPackagesFlagName, "allowed")
+
+	if err != nil {
+		t.FailNow()
+	}
+
+	testdata, err := filepath.Abs("testdata/allowed")
+	if err != nil {
+		t.FailNow()
+	}
+
+	analysistest.Run(t, testdata, analyzer)
+}
+
 func TestAnalyzer_InvalidRegexp(t *testing.T) {
 	invalid := `\Ca`
 	analyzer := testpackage.NewAnalyzer()