feat: add end-to-end tests for sqlcmd binary (fixes microsoft#641)

Add e2e tests that build the sqlcmd binary and exercise real-world scenarios:

Non-connection tests (always run):
- TestE2E_Help: verifies --help flag works
- TestE2E_Version: verifies --version flag works
- TestE2E_PipedInput_NoPanic: regression test for microsoft#607 (piped input panic)
- TestE2E_PipedInput_EmptyInput: empty piped input doesn't panic
- TestE2E_InvalidFlag: invalid flags produce helpful errors
- TestE2E_QueryFlag_NoServer: -Q flag without server doesn't panic
- TestE2E_InputFile_NotFound: missing input file errors gracefully
- TestE2E_PipedInput_WithStdinReader: GO batches in piped input work

Live connection tests (run when SQLCMDSERVER is set):
- TestE2E_PipedInput_LiveConnection: piped SQL with real server
- TestE2E_QueryFlag_LiveConnection: -Q flag with real server
- TestE2E_InputFile_LiveConnection: -i flag with real server

The tests build the binary once and reuse it for all tests.
Live connection tests use SQLCMDSERVER, SQLCMDUSER, SQLCMDPASSWORD env vars.

Addresses feedback from @shueybubbles in PR microsoft#640.

Author: dlevy-msft-sql

cmd/modern/e2e_test.go

@@ -0,0 +1,287 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+package main
+
+import (
+	"bytes"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	binaryPath string
+	buildOnce  sync.Once
+	buildErr   error
+)
+
+// buildBinary compiles the sqlcmd binary once for all e2e tests.
+// The binary is placed in a temporary directory and cleaned up after tests complete.
+func buildBinary(t *testing.T) string {
+	t.Helper()
+	buildOnce.Do(func() {
+		tmpDir, err := os.MkdirTemp("", "sqlcmd-e2e-*")
+		if err != nil {
+			buildErr = err
+			return
+		}
+
+		binaryName := "sqlcmd"
+		if runtime.GOOS == "windows" {
+			binaryName = "sqlcmd.exe"
+		}
+		binaryPath = filepath.Join(tmpDir, binaryName)
+
+		cmd := exec.Command("go", "build", "-o", binaryPath, ".")
+		// Build from the cmd/modern directory
+		wd, err := os.Getwd()
+		if err != nil {
+			buildErr = err
+			return
+		}
+		cmd.Dir = wd
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			buildErr = &buildError{err: err, output: string(output)}
+			return
+		}
+	})
+	if buildErr != nil {
+		t.Fatalf("Failed to build sqlcmd binary: %v", buildErr)
+	}
+	return binaryPath
+}
+
+// hasLiveConnection returns true if SQLCMDSERVER environment variable is set,
+// indicating a live SQL Server connection is available for testing.
+func hasLiveConnection() bool {
+	return os.Getenv("SQLCMDSERVER") != ""
+}
+
+// skipIfNoLiveConnection skips the test if no live SQL Server connection is available.
+func skipIfNoLiveConnection(t *testing.T) {
+	t.Helper()
+	if !hasLiveConnection() {
+		t.Skip("Skipping: SQLCMDSERVER not set, no live connection available")
+	}
+}
+
+type buildError struct {
+	err    error
+	output string
+}
+
+func (e *buildError) Error() string {
+	return e.err.Error() + ": " + e.output
+}
+
+// TestE2E_Help verifies that --help flag works and produces expected output.
+func TestE2E_Help(t *testing.T) {
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "--help")
+	output, err := cmd.CombinedOutput()
+
+	require.NoError(t, err, "sqlcmd --help should not error")
+	assert.Contains(t, string(output), "sqlcmd", "help output should mention sqlcmd")
+	assert.Contains(t, string(output), "Usage:", "help output should contain Usage section")
+}
+
+// TestE2E_Version verifies that --version flag works.
+func TestE2E_Version(t *testing.T) {
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "--version")
+	output, err := cmd.CombinedOutput()
+
+	require.NoError(t, err, "sqlcmd --version should not error")
+	// Version output should contain version info
+	outputStr := string(output)
+	assert.True(t, strings.Contains(outputStr, "Version") || strings.Contains(outputStr, "version") || strings.Contains(outputStr, "v"),
+		"version output should contain version info: %s", outputStr)
+}
+
+// TestE2E_PipedInput_NoPanic verifies that piping input to sqlcmd with -G flag
+// does not cause a nil pointer panic. This is a regression test for issue #607.
+// The command will fail to connect because it targets a non-existent server, but it should
+// NOT panic - that's the key behavior we're testing.
+func TestE2E_PipedInput_NoPanic(t *testing.T) {
+	binary := buildBinary(t)
+
+	// Create a command that pipes input
+	cmd := exec.Command(binary, "-G", "-S", "nonexistent.database.windows.net", "-d", "testdb")
+	cmd.Stdin = strings.NewReader("SELECT 1\nGO\n")
+
+	// Run the command - we expect it to fail (can't connect), but NOT panic
+	output, err := cmd.CombinedOutput()
+	outputStr := string(output)
+
+	// The command should fail with a connection error, not a panic
+	if err != nil {
+		// This is expected - we can't connect to a non-existent server
+		// But we should NOT see a panic in the output
+		assert.NotContains(t, outputStr, "panic:", "sqlcmd should not panic when piping input")
+		assert.NotContains(t, outputStr, "nil pointer", "sqlcmd should not have nil pointer error")
+		assert.NotContains(t, outputStr, "runtime error", "sqlcmd should not have runtime error")
+	}
+	// If it somehow succeeded (unlikely), that's fine too
+}
+
+// TestE2E_PipedInput_LiveConnection tests piping input with a real SQL Server connection.
+// This test only runs when SQLCMDSERVER is set.
+func TestE2E_PipedInput_LiveConnection(t *testing.T) {
+	skipIfNoLiveConnection(t)
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "-C")
+	cmd.Stdin = strings.NewReader("SELECT 1 AS TestValue\nGO\n")
+	cmd.Env = os.Environ() // Inherit SQLCMDSERVER, SQLCMDUSER, SQLCMDPASSWORD
+
+	output, err := cmd.CombinedOutput()
+	outputStr := string(output)
+
+	require.NoError(t, err, "piped query should succeed with live connection: %s", outputStr)
+	assert.Contains(t, outputStr, "TestValue", "output should contain column name")
+	assert.Contains(t, outputStr, "1", "output should contain query result")
+}
+
+// TestE2E_PipedInput_EmptyInput verifies that piping empty input doesn't panic.
+func TestE2E_PipedInput_EmptyInput(t *testing.T) {
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "-S", "nonexistent.server")
+	cmd.Stdin = strings.NewReader("")
+
+	output, err := cmd.CombinedOutput()
+	outputStr := string(output)
+
+	// Should fail with connection error, not panic
+	if err != nil {
+		assert.NotContains(t, outputStr, "panic:", "sqlcmd should not panic with empty piped input")
+		assert.NotContains(t, outputStr, "nil pointer", "sqlcmd should not have nil pointer error")
+	}
+}
+
+// TestE2E_InvalidFlag verifies that invalid flags produce a helpful error message.
+func TestE2E_InvalidFlag(t *testing.T) {
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "--this-flag-does-not-exist")
+	output, err := cmd.CombinedOutput()
+
+	assert.Error(t, err, "invalid flag should cause an error")
+	outputStr := string(output)
+	// Should have some kind of error message about unknown flag
+	assert.True(t, strings.Contains(outputStr, "unknown") || strings.Contains(outputStr, "invalid") || strings.Contains(outputStr, "flag"),
+		"error message should indicate unknown/invalid flag: %s", outputStr)
+}
+
+// TestE2E_QueryFlag_NoServer verifies -Q flag behavior without a server.
+func TestE2E_QueryFlag_NoServer(t *testing.T) {
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "-Q", "SELECT 1")
+	output, err := cmd.CombinedOutput()
+	outputStr := string(output)
+
+	// Should fail because no server is specified, but not panic
+	if err != nil {
+		assert.NotContains(t, outputStr, "panic:", "sqlcmd should not panic")
+	}
+}
+
+// TestE2E_QueryFlag_LiveConnection tests the -Q flag with a real SQL Server connection.
+// This test only runs when SQLCMDSERVER is set.
+func TestE2E_QueryFlag_LiveConnection(t *testing.T) {
+	skipIfNoLiveConnection(t)
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "-C", "-Q", "SELECT 42 AS Answer")
+	cmd.Env = os.Environ()
+
+	output, err := cmd.CombinedOutput()
+	outputStr := string(output)
+
+	require.NoError(t, err, "-Q query should succeed: %s", outputStr)
+	assert.Contains(t, outputStr, "Answer", "output should contain column name")
+	assert.Contains(t, outputStr, "42", "output should contain query result")
+}
+
+// TestE2E_InputFile_NotFound verifies proper error when input file doesn't exist.
+func TestE2E_InputFile_NotFound(t *testing.T) {
+	binary := buildBinary(t)
+
+	cmd := exec.Command(binary, "-i", "/nonexistent/path/to/file.sql", "-S", "localhost")
+	output, err := cmd.CombinedOutput()
+
+	assert.Error(t, err, "non-existent input file should cause an error")
+	outputStr := string(output)
+	assert.NotContains(t, outputStr, "panic:", "should not panic on missing input file")
+}
+
+// TestE2E_InputFile_LiveConnection tests the -i flag with a real SQL Server connection.
+// This test only runs when SQLCMDSERVER is set.
+func TestE2E_InputFile_LiveConnection(t *testing.T) {
+	skipIfNoLiveConnection(t)
+	binary := buildBinary(t)
+
+	// Create a temporary SQL file
+	tmpFile, err := os.CreateTemp("", "e2e-test-*.sql")
+	require.NoError(t, err)
+	defer os.Remove(tmpFile.Name())
+
+	_, err = tmpFile.WriteString("SELECT 'InputFileTest' AS Source\nGO\n")
+	require.NoError(t, err)
+	require.NoError(t, tmpFile.Close())
+
+	cmd := exec.Command(binary, "-C", "-i", tmpFile.Name())
+	cmd.Env = os.Environ()
+
+	output, err := cmd.CombinedOutput()
+	outputStr := string(output)
+
+	require.NoError(t, err, "-i input file should succeed: %s", outputStr)
+	assert.Contains(t, outputStr, "InputFileTest", "output should contain query result from input file")
+}
+
+// TestE2E_PipedInput_WithBytesBuffer_NoPanic verifies that piping from bytes.Buffer
+// into stdin does not cause a panic, even when the connection fails.
+func TestE2E_PipedInput_WithBytesBuffer_NoPanic(t *testing.T) {
+	binary := buildBinary(t)
+
+	input := bytes.NewBufferString("SELECT @@VERSION\nGO\n")
+	cmd := exec.Command(binary, "-S", "nonexistent.server", "-C")
+	cmd.Stdin = input
+
+	output, err := cmd.CombinedOutput()
+	outputStr := string(output)
+
+	// Should fail to connect, but not panic
+	if err != nil {
+		assert.NotContains(t, outputStr, "panic:", "should not panic when piping SQL with GO")
+		assert.NotContains(t, outputStr, "nil pointer", "should not have nil pointer error")
+	}
+}
+
+// cleanupBinary removes the temporary build directory containing the test binary.
+// TestMain calls this to ensure deterministic cleanup instead of relying on
+// eventual OS temp directory maintenance.
+func cleanupBinary() {
+	if binaryPath != "" {
+		os.RemoveAll(filepath.Dir(binaryPath))
+	}
+}
+
+func TestMain(m *testing.M) {
+	code := m.Run()
+	cleanupBinary()
+	os.Exit(code)
+}