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Run DBI queries against a mocked database

Source: R/mock-db.R
mockdb.Rd

Wrap a chunk of code in with_mock_db() to use mocked databases that will use fixtures instead of connecting to a real database. Alternatively, you can start and stop using a mocked database with start_mock_db() and stop_mock_db() respectively.to execute the whole thing without needing to remember to stop the mocking. When testing with dittodb, it will look for fixtures in all entries of db_mock_paths.

Usage

with_mock_db(expr)

start_mock_db()

stop_mock_db()

Arguments

expr

the expression to execute

Value

nothing

Details

You only need to use one approach: either use start_mock_db() to start using mocks and then stop_mock_db() to stop or use with_mock_db() wrapped around the code you want to execute against the mocked database. You don't need to (and should not) use both at the same time. Generally with_mock_db() is preferred because it is slightly safer and you don't have to remember to stop_mock_db() when you're done. However, it is easier to step through tests interactively using start_mock_db()/stop_mock_db().

Connections should be made after start_mock_db() if you're using that function or they should be made inside of with_mock_db() if you're using that function because dittodb uses the database name (given in dbname or Database argument of dbConnect depending on the driver) to separate different fixtures. For ODBC connections with only a dsn provided, the dsn is used for this directory.

Examples

# Add the mocks included with dittodb to the db_mock_paths to use them below
db_mock_paths(system.file("nycflight_mocks", package = "dittodb"), last = TRUE)

if (check_for_pkg("RSQLite", message) & check_for_pkg("testthat", message)) {
  # using  `with_mock_db()`
  with_mock_db({
    con <- dbConnect(
      RSQLite::SQLite(),
      dbname = "nycflights"
    )

    testthat::test_that("We get one airline", {
      one_airline <- dbGetQuery(
        con,
        "SELECT carrier, name FROM airlines LIMIT 1"
      )
      testthat::expect_s3_class(one_airline, "data.frame")
      testthat::expect_equal(nrow(one_airline), 1)
      testthat::expect_equal(one_airline$carrier, "9E")
      testthat::expect_equal(one_airline$name, "Endeavor Air Inc.")
    })

    dbDisconnect(con)
  })

  # using `start_mock_db()` and `stop_mock_db()`
  start_mock_db()
  con <- dbConnect(
    RSQLite::SQLite(),
    dbname = "nycflights"
  )

  testthat::test_that("We get one airline", {
    one_airline <- dbGetQuery(
      con,
      "SELECT carrier, name FROM airlines LIMIT 1"
    )
    testthat::expect_s3_class(one_airline, "data.frame")
    testthat::expect_equal(nrow(one_airline), 1)
    testthat::expect_equal(one_airline$carrier, "9E")
    testthat::expect_equal(one_airline$name, "Endeavor Air Inc.")
  })

  dbDisconnect(con)
  stop_mock_db()
}
#> Test passed 😀
#> Test passed 🥇