Add option to run Go tests automatically

README.md

@@ -16,12 +16,15 @@ go install github.com/konradreiche/coverdiff@latest
 ```
 Usage:
 	coverdiff [file]
+	coverdiff test
 
 Flags:
 	-h, --help	print help text
 
 Examples:
 
+	coverdiff test
+
 	go test -cover -coverprofile=coverage.out
 	cat coverage.out | coverdiff
 

command.go

@@ -1,15 +1,35 @@
 package main
 
 import (
+	"flag"
+	"fmt"
 	"io"
 	"os"
+	"os/exec"
 
 	"golang.org/x/tools/cover"
 )
 
 func command(stdin io.Reader, stdout io.Writer) error {
+	var (
+		fileName string
+		err      error
+	)
+	switch flag.CommandLine.Arg(0) {
+	case "test":
+		fileName, err = runGoTests()
+		if err != nil {
+			return err
+		}
+		defer deleteTempFile(fileName)
+	case "-":
+	// user explicitly specified to use stdin
+	default:
+		fileName = flag.CommandLine.Arg(0)
+	}
+
 	// parse coverage profiles from stdin or file path if provided
-	profiles, err := parseCoverProfiles(stdin)
+	profiles, err := parseCoverProfiles(fileName, stdin)
 	if err != nil {
 		return err
 	}
@@ -23,9 +43,28 @@ func command(stdin io.Reader, stdout io.Writer) error {
 	return printDiff(stdout, profiles, moduleInfo)
 }
 
-func parseCoverProfiles(stdin io.Reader) ([]*cover.Profile, error) {
-	if len(os.Args) > 1 && os.Args[1] != "-" {
-		profiles, err := cover.ParseProfiles(os.Args[1])
+func runGoTests() (string, error) {
+	f, err := os.CreateTemp(os.TempDir(), "coverdiff-*")
+	if err != nil {
+		return "", err
+	}
+	cmd := exec.Command("go", "test", "./...", "-cover", "-coverprofile="+f.Name())
+	if err := cmd.Run(); err != nil {
+		return "", err
+	}
+	return f.Name(), nil
+}
+
+func deleteTempFile(fileName string) {
+	if err := os.Remove(fileName); err != nil {
+		fmt.Fprintln(os.Stderr, fmt.Errorf("coverdiff: %w", err))
+		os.Exit(1)
+	}
+}
+
+func parseCoverProfiles(fileName string, stdin io.Reader) ([]*cover.Profile, error) {
+	if fileName != "" {
+		profiles, err := cover.ParseProfiles(fileName)
 		return profiles, err
 	}
 	profiles, err := cover.ParseProfilesFromReader(stdin)

command_test.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"flag"
 	"os"
 	"path/filepath"
 	"testing"
@@ -16,6 +17,24 @@ func TestCommand(t *testing.T) {
 		os.Args = []string{
 			"coverdiff",
 		}
+		flag.Parse()
+
+		var stdout bytes.Buffer
+		stdin := bytes.NewBufferString(readFile(t, "testdata/coverage.out"))
+		if err := command(stdin, &stdout); err != nil {
+			t.Fatal(err)
+		}
+
+		got := stdout.String()
+		want := readFile(t, "testdata/coverdiff.out")
+		if got != want {
+			t.Errorf("got len=%d, want len=%d", len(got), len(want))
+		}
+	})
+
+	t.Run("from-stdin-dash", func(t *testing.T) {
+		os.Args[1] = "-"
+		flag.Parse()
 
 		var stdout bytes.Buffer
 		stdin := bytes.NewBufferString(readFile(t, "testdata/coverage.out"))
@@ -32,6 +51,7 @@ func TestCommand(t *testing.T) {
 
 	t.Run("from-file", func(t *testing.T) {
 		os.Args[1] = filepath.Join(projectPath, "testdata/coverage.out")
+		flag.Parse()
 
 		var stdout bytes.Buffer
 		if err := command(nil, &stdout); err != nil {
@@ -55,6 +75,7 @@ func TestCommand(t *testing.T) {
 			}
 		})
 		os.Args[1] = filepath.Join(projectPath, "testdata/coverage.out")
+		flag.Parse()
 
 		var stdout bytes.Buffer
 		if err := command(nil, &stdout); err != nil {
@@ -80,6 +101,24 @@ func TestCommand(t *testing.T) {
 			t.Errorf("got %s, want: %s", got, want)
 		}
 	})
+
+	t.Run("run-go-tests", func(t *testing.T) {
+		os.Args[1] = "test"
+		flag.Parse()
+
+		changeDir(t, "testdata")
+
+		var stdout bytes.Buffer
+		if err := command(nil, &stdout); err != nil {
+			t.Fatal(err)
+		}
+
+		got := stdout.String()
+		want := readFile(t, "coverdiff.out")
+		if got != want {
+			t.Errorf("got len=%d, want len=%d", len(got), len(want))
+		}
+	})
 }
 
 func readFile(tb testing.TB, name string) string {

help.go

@@ -9,17 +9,20 @@ const usage = `📑 coverdiff - print Go test coverage as diff
 
 Usage:
 	coverdiff [file]
+	coverdiff test
 
 Flags:
 	-h, --help	print help text
 
-coverdiff is a tool designed to process the cover profile output of Go and
-display the coverage as a diff, similar to Go's -html option but optimized for
-terminal convenience. You can provide the cover profile as a file or pass it
-through standard input.
+coverdiff is a tool that processes Go cover profiles and displays coverage
+differences directly on the terminal, similar to Go's -html option. You can
+provide the cover profile as a file, pass it through standard input, or let
+coverdiff run the Go tests.
 
 Examples:
 
+	coverdiff test
+
 	go test -cover -coverprofile=coverage.out
 	cat coverage.out | coverdiff