Add testpackage analyzer

.gitignore

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+.idea/
+.DS_Store
+*.out

.travis.yml

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+language: go
+go:
+  - "1.11.x"
+  - "1.12.x"
+env:
+  global:
+    - GO111MODULE=on
+matrix:
+  include:
+    - go: "1.13.x"
+      #install:
+      #  - curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.21.0
+      #  - golangci-lint --version
+      script:
+        - go test -race -coverpkg ./... -coverprofile=coverage.out ./...
+
+        #- golangci-lint run
+
+        - echo "Check that go.mod and go.sum are tidy"
+        - go mod tidy
+        - if [[ `git status --porcelain go.mod` ]]; then git diff -- go.mod ; echo "go.mod is outdated, please run go mod tidy" ; exit 1; fi
+        - if [[ `git status --porcelain go.sum` ]]; then git diff -- go.sum ; echo "go.sum is outdated, please run go mod tidy" ; exit 1; fi
+      after_success:
+        - bash <(curl -s https://codecov.io/bash)
+script:
+  - go test -race ./...

go.mod

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+module github.com/maratori/testpackage
+
+go 1.13
+
+require golang.org/x/tools v0.0.0-20191101200257-8dbcdeb83d3f

go.sum

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+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20191101200257-8dbcdeb83d3f h1:+QO45yvqhfD79HVNFPAgvstYLFye8zA+rd0mHFsGV9s=
+golang.org/x/tools v0.0.0-20191101200257-8dbcdeb83d3f/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

main.go

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+package main
+
+import (
+	"golang.org/x/tools/go/analysis/singlechecker"
+
+	"github.com/maratori/testpackage/pkg/testpackage"
+)
+
+func main() {
+	singlechecker.Main(testpackage.Analyzer)
+}

pkg/testpackage/testdata/bad/bad.go

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+package bad

pkg/testpackage/testdata/bad/bad_test.go

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+package bad // want `package should be "bad_test" instead of "bad"`

pkg/testpackage/testdata/bad/good_inside_bad_test.go

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+package bad_test

pkg/testpackage/testdata/good/good.go

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+package good

pkg/testpackage/testdata/good/good_test.go

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+package good_test

pkg/testpackage/testpackage.go

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+package testpackage
+
+import (
+	"strings"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+// Analyzer that make you use a separate _test package
+var Analyzer = &analysis.Analyzer{
+	Name: "testpackage",
+	Doc:  "linter that make you use a separate _test package",
+	Run:  run,
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	for _, f := range pass.Files {
+		fileName := pass.Fset.Position(f.Pos()).Filename
+		if strings.HasSuffix(fileName, "_test.go") {
+			packageName := f.Name.Name
+			if !strings.HasSuffix(packageName, "_test") {
+				pass.Reportf(f.Pos(), `package should be "%s_test" instead of "%s"`, packageName, packageName)
+			}
+		}
+	}
+	return nil, nil
+}

pkg/testpackage/testpackage_test.go

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+package testpackage_test
+
+import (
+	"path/filepath"
+	"testing"
+
+	"golang.org/x/tools/go/analysis/analysistest"
+
+	"github.com/maratori/testpackage/pkg/testpackage"
+)
+
+func TestAnalyzer_Good(t *testing.T) {
+	testdata, err := filepath.Abs("testdata/good")
+	if err != nil {
+		t.FailNow()
+	}
+	analysistest.Run(t, testdata, testpackage.Analyzer)
+}
+
+func TestAnalyzer_Bad(t *testing.T) {
+	testdata, err := filepath.Abs("testdata/bad")
+	if err != nil {
+		t.FailNow()
+	}
+	analysistest.Run(t, testdata, testpackage.Analyzer)
+}