Crussell/backend/db/error_injector_test.go

//go:build test

package db

import (
	"context"
	"errors"
	"testing"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgconn"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// =============================================================================
// FailingTx — wraps a real pgx.Tx and fails on configured operations
// =============================================================================

// FailingTx wraps a pgx.Tx and injects failures on configured operations.
// All unmodified methods delegate to the real transaction via embedding.
type FailingTx struct {
	pgx.Tx                          // delegate all methods to real tx
	failBegin  bool                 // return self instead of savepoint
	failExec   bool
	failCommit bool
	execErr    error
	commitErr  error
}

// Begin returns self instead of creating a savepoint, so subsequent
// Exec/Commit calls go through our wrapper's failure checks.
func (f *FailingTx) Begin(ctx context.Context) (pgx.Tx, error) {
	if f.failBegin {
		return nil, errors.New("simulated begin failure")
	}
	return f, nil
}

// Exec fails with the configured error if failExec is true.
func (f *FailingTx) Exec(ctx context.Context, sql string, args ...any) (pgconn.CommandTag, error) {
	if f.failExec {
		return pgconn.CommandTag{}, f.execErr
	}
	return f.Tx.Exec(ctx, sql, args...)
}

// Commit fails with the configured error if failCommit is true.
func (f *FailingTx) Commit(ctx context.Context) error {
	if f.failCommit {
		return f.commitErr
	}
	return f.Tx.Commit(ctx)
}

// =============================================================================
// FailingPoolProxy — wraps *PoolProxy and returns FailingTx from Begin
// =============================================================================

// FailingPoolProxy wraps a *PoolProxy and overrides Begin to return a
// FailingTx that can fail on Exec or Commit. All other methods (Exec,
// Query, QueryRow, Ping, Acquire) delegate to the embedded PoolProxy.
type FailingPoolProxy struct {
	*PoolProxy
	failExec   bool
	failCommit bool
	execErr    error
	commitErr  error
}

// Begin starts a transaction wrapped in a FailingTx that respects the
// configured failure modes. If the underlying Begin fails, the error
// propagates as-is.
func (f *FailingPoolProxy) Begin(ctx context.Context) (pgx.Tx, error) {
	realTx, err := f.PoolProxy.Begin(ctx)
	if err != nil {
		return nil, err
	}
	return &FailingTx{
		Tx:         realTx,
		failExec:   f.failExec,
		failCommit: f.failCommit,
		execErr:    f.execErr,
		commitErr:  f.commitErr,
	}, nil
}

// =============================================================================
// WithFailingConn — convenience constructor for FailingPoolProxy
// =============================================================================

// WithFailingConn creates a FailingPoolProxy with default error messages
// and the given failure modes.
func WithFailingConn(original *PoolProxy, failExec, failCommit bool) *FailingPoolProxy {
	return &FailingPoolProxy{
		PoolProxy:  original,
		failExec:   failExec,
		failCommit: failCommit,
		execErr:    errors.New("simulated exec failure"),
		commitErr:  errors.New("simulated commit failure"),
	}
}

// =============================================================================
// Tests
// =============================================================================

func TestFailingTx_ExecFailure(t *testing.T) {
	closePool()
	resetEnv()
	err := Connect()
	require.NoError(t, err)
	defer closePool()

	ctx := context.Background()
	pool := Conn.Pool()
	realTx, err := pool.Begin(ctx)
	require.NoError(t, err)
	defer realTx.Rollback(ctx) //nolint:errcheck

	ftx := &FailingTx{Tx: realTx, failExec: true, execErr: errors.New("disk full")}

	// Begin returns self
	tx2, err := ftx.Begin(ctx)
	require.NoError(t, err)
	_, ok := tx2.(*FailingTx)
	assert.True(t, ok, "should return FailingTx")

	// Exec fails
	_, err = ftx.Exec(ctx, "SELECT 1")
	assert.ErrorContains(t, err, "disk full")

	// Commit still works (not set to fail)
	err = ftx.Commit(ctx)
	assert.NoError(t, err)
}

func TestFailingTx_CommitFailure(t *testing.T) {
	closePool()
	resetEnv()
	err := Connect()
	require.NoError(t, err)
	defer closePool()

	ctx := context.Background()
	pool := Conn.Pool()
	realTx, err := pool.Begin(ctx)
	require.NoError(t, err)
	defer realTx.Rollback(ctx) //nolint:errcheck

	ftx := &FailingTx{Tx: realTx, failCommit: true, commitErr: errors.New("commit failed")}

	// Exec works (not set to fail)
	_, err = ftx.Exec(ctx, "SELECT 1")
	assert.NoError(t, err)

	// Commit fails
	err = ftx.Commit(ctx)
	assert.ErrorContains(t, err, "commit failed")
}

func TestFailingPoolProxy_BeginReturnsFailingTx(t *testing.T) {
	closePool()
	resetEnv()
	err := Connect()
	require.NoError(t, err)
	defer closePool()

	ctx := context.Background()

	fp := &FailingPoolProxy{
		PoolProxy:  Conn,
		failCommit: true,
		commitErr:  errors.New("commit failed"),
	}

	tx, err := fp.Begin(ctx)
	require.NoError(t, err)
	defer tx.Rollback(ctx) //nolint:errcheck

	_, ok := tx.(*FailingTx)
	assert.True(t, ok, "should return FailingTx")

	// Exec works (not set to fail)
	_, err = tx.Exec(ctx, "SELECT 1")
	assert.NoError(t, err)

	// Commit fails
	err = tx.Commit(ctx)
	assert.ErrorContains(t, err, "commit failed")
}