x/auth: turn sign --validate-sigantures into a standalone command (#6108)

--validate-signatures should not be a flag of the sign command
as the operation performed (transaction signatures verification)
is logically distinct.

cli_test is and has always been an horrible name for package
directory as it's very much Go anti-idiomatic - _test is the
suffix used by test packages, not directories. Plus, CLI test
cases can and should live alongside other testcases that don't
require binaries to be built beforehand. Thus:

x/module/client/cli_test/*.go -> x/module/client/cli/

Test files that require sim{cli,d} shall be tagged with // +build cli_test

With regard to cli test auxiliary functions, they should live in:

x/module/client/testutil/

Co-authored-by: Alexander Bezobchuk <alexanderbez@users.noreply.github.com>

x/auth/client/cli/cli_test.go

@@ -0,0 +1,68 @@
+// +build cli_test
+
+package cli_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/cosmos/cosmos-sdk/tests"
+	"github.com/cosmos/cosmos-sdk/tests/cli"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/x/auth/client/testutil"
+)
+
+func TestCLIValidateSignatures(t *testing.T) {
+	t.Parallel()
+	f := cli.InitFixtures(t)
+
+	// start simd server
+	proc := f.SDStart()
+	t.Cleanup(func() { proc.Stop(false) })
+
+	f.ValidateGenesis()
+
+	fooAddr := f.KeyAddress(cli.KeyFoo)
+	barAddr := f.KeyAddress(cli.KeyBar)
+
+	// generate sendTx with default gas
+	success, stdout, stderr := testutil.TxSend(f, fooAddr.String(), barAddr, sdk.NewInt64Coin("stake", 10), "--generate-only")
+	require.True(t, success)
+	require.Empty(t, stderr)
+
+	// write  unsigned tx to file
+	unsignedTxFile, cleanup := tests.WriteToNewTempFile(t, stdout)
+	t.Cleanup(cleanup)
+
+	// validate we can successfully sign
+	success, stdout, _ = testutil.TxSign(f, cli.KeyFoo, unsignedTxFile.Name())
+	require.True(t, success)
+
+	stdTx := cli.UnmarshalStdTx(t, f.Cdc, stdout)
+
+	require.Equal(t, len(stdTx.Msgs), 1)
+	require.Equal(t, 1, len(stdTx.GetSignatures()))
+	require.Equal(t, fooAddr.String(), stdTx.GetSigners()[0].String())
+
+	// write signed tx to file
+	signedTxFile, cleanup := tests.WriteToNewTempFile(t, stdout)
+	t.Cleanup(cleanup)
+
+	// validate signatures
+	success, _, _ = testutil.TxValidateSignatures(f, signedTxFile.Name())
+	require.True(t, success)
+
+	// modify the transaction
+	stdTx.Memo = "MODIFIED-ORIGINAL-TX-BAD"
+	bz := cli.MarshalStdTx(t, f.Cdc, stdTx)
+	modSignedTxFile, cleanup := tests.WriteToNewTempFile(t, string(bz))
+	t.Cleanup(cleanup)
+
+	// validate signature validation failure due to different transaction sig bytes
+	success, _, _ = testutil.TxValidateSignatures(f, modSignedTxFile.Name())
+	require.False(t, success)
+
+	// Cleanup testing directories
+	f.Cleanup()
+}