TDD Workflow

# R/calculate_ci.R

#' Calculate Bootstrap Confidence Interval
#'
#' @param x Numeric vector
#' @param conf_level Confidence level (default 0.95)
#' @param n_boot Number of bootstrap samples (default 1000)
#' @return Named numeric vector with lower and upper bounds
#' @export
calculate_ci <- function(x, conf_level = 0.95, n_boot = 1000) {
  # Validate inputs
  if (!is.numeric(x)) {
    cli::cli_abort("{.arg x} must be numeric", class = "validation_error")
  }
  if (length(x) == 0) {
    cli::cli_abort("{.arg x} cannot be empty", class = "validation_error")
  }
  if (conf_level <= 0 || conf_level >= 1) {
    cli::cli_abort("{.arg conf_level} must be between 0 and 1", class = "validation_error")
  }

  # Remove NA values
  x <- x[!is.na(x)]

  # Bootstrap
  boot_means <- replicate(n_boot, mean(sample(x, replace = TRUE)))

  # Calculate quantiles
  alpha <- 1 - conf_level
  c(
    lower = unname(quantile(boot_means, alpha / 2)),
    upper = unname(quantile(boot_means, 1 - alpha / 2))
  )
}

devtools::test()
# ✔ calculate_ci returns correct structure
# ✔ calculate_ci respects confidence level
# ✔ calculate_ci handles NA values
# ✔ calculate_ci validates inputs

# Extract validation to helper
validate_ci_inputs <- function(x, conf_level) {
  if (!is.numeric(x)) {
    cli::cli_abort("{.arg x} must be numeric", class = "validation_error")
  }
  if (length(x) == 0) {
    cli::cli_abort("{.arg x} cannot be empty", class = "validation_error")
  }
  if (conf_level <= 0 || conf_level >= 1) {
    cli::cli_abort("{.arg conf_level} must be between 0 and 1", class = "validation_error")
  }
}

calculate_ci <- function(x, conf_level = 0.95, n_boot = 1000) {
  validate_ci_inputs(x, conf_level)

  x <- x[!is.na(x)]
  boot_means <- replicate(n_boot, mean(sample(x, replace = TRUE)))

  alpha <- 1 - conf_level
  c(
    lower = unname(quantile(boot_means, alpha / 2)),
    upper = unname(quantile(boot_means, 1 - alpha / 2))
  )
}

covr::package_coverage()
# calculate_ci.R: 100%

test_that("clean_data removes invalid rows", {
  input <- tibble(
    id = 1:4,
    value = c(1, NA, 3, -999)
  )

  result <- clean_data(input, invalid_value = -999)

  expect_equal(nrow(result), 2)
  expect_equal(result$id, c(1, 3))
  expect_false(anyNA(result$value))
})

test_that("weighted_mean matches manual calculation", {
  x <- c(1, 2, 3)
  w <- c(1, 2, 1)

  result <- weighted_mean(x, w)
  expected <- sum(x * w) / sum(w)  # (1 + 4 + 3) / 4 = 2

  expect_equal(result, expected)
})

# helper-fixtures.R
read_fixture <- function(name) {
  path <- testthat::test_path("fixtures", name)
  readr::read_csv(path, show_col_types = FALSE)
}

# test-pipeline.R
test_that("pipeline handles real data", {
  input <- read_fixture("sample_data.csv")
  result <- process_pipeline(input)

  expect_snapshot(result)
})

test_that("fetch_data handles API errors", {
  # Mock the API call
  local_mocked_bindings(
    httr2_request = function(...) {
      stop("API unavailable")
    }
  )

  expect_error(
    fetch_data("endpoint"),
    "API unavailable"
  )
})

test_that("function respects options", {
  # Temporarily set options
  withr::local_options(list(digits = 2))

  result <- format_number(3.14159)
  expect_equal(result, "3.14")
})

test_that("function writes to temp file", {
  # Create temp file that's automatically cleaned up
  tmp <- withr::local_tempfile(lines = c("line 1", "line 2"))

  result <- process_file(tmp)
  expect_equal(result$n_lines, 2)
})

test_that("function uses custom environment variable", {
  # Temporarily set env var
  withr::local_envvar(MY_VAR = "test_value")

  result <- get_config()
  expect_equal(result$my_var, "test_value")
})

# helper-data.R
make_sample_data <- function(n = 100) {
  tibble(
    id = 1:n,
    group = sample(c("A", "B"), n, replace = TRUE),
    value = rnorm(n)
  )
}

# test-analysis.R
test_that("analysis handles grouped data", {
  data <- make_sample_data(n = 50)
  result <- analyze_groups(data)
  expect_s3_class(result, "tbl_df")
})

test_that("function reads CSV correctly", {
  # Create temp file with cleanup
  tmp <- withr::local_tempfile(fileext = ".csv")
  write.csv(mtcars, tmp, row.names = FALSE)

  result <- read_and_process(tmp)
  expect_equal(nrow(result), 32)
})

# Store in: tests/testthat/fixtures/sample_data.csv

test_that("function handles real data format", {
  path <- test_path("fixtures", "sample_data.csv")
  data <- read_csv(path)
  result <- process_data(data)
  expect_true(all(result$valid))
})

# Don't test internal state
expect_equal(obj$internal_cache, expected_cache)

# Test observable behavior
expect_equal(get_result(obj), expected_result)

# Breaks on any output change
expect_equal(as.character(result), "Mean: 5.234567890")

# Robust to formatting changes
expect_equal(result$mean, 5.23, tolerance = 0.01)

test_that("creates data", { global_data <<- create() })
test_that("uses data", { process(global_data) })  # Depends on previous!

test_that("creates and uses data", {
  data <- create()
  result <- process(data)
  expect_true(is_valid(result))
})

# When a test fails, don't change the test (unless it's wrong)
test_that("function returns 42", {
  expect_equal(my_function(), 42)  # Test fails
})

# DON'T DO THIS:
test_that("function returns 41", {
  expect_equal(my_function(), 41)  # Changed to pass - WRONG!
})

# Fix the code to match expected behavior
test_that("function returns 42", {
  expect_equal(my_function(), 42)  # Test fails
})

# Fix my_function() implementation instead

# Review and accept snapshot changes
testthat::snapshot_review("test_name")
testthat::snapshot_accept("test_name")

# Run coverage report
covr::package_coverage()

# Interactive HTML report
covr::report()

# Check specific thresholds
cov <- covr::package_coverage()
pct <- covr::percent_coverage(cov)
if (pct < 80) {
  stop("Coverage below 80%: ", round(pct, 1), "%")
}

# In testthat.R or as a coverage check
covr::package_coverage(
  type = "all",
  line_coverage = 0.80,
  function_coverage = 0.80
)

# Micro: Interactive development
devtools::load_all()
expect_equal(my_function(1), 1)  # Direct expectation

# Mezzo: Single file
testthat::test_file("tests/testthat/test-validation.R")
# RStudio: Ctrl/Cmd+Shift+T

# Macro: Full suite
devtools::test()
devtools::check()  # Full package validation

# Find slow tests
devtools::test(reporter = "slow")

# Progress reporter (verbose)
devtools::test(reporter = "progress")

# Test execution order independence
devtools::test(shuffle = TRUE)

# Watch mode - auto-run on file changes
testthat::auto_test_package()

# All tests
devtools::test()

# All tests (keyboard shortcut)
# RStudio: Ctrl/Cmd+Shift+T

# With coverage
covr::package_coverage()

# Specific file
testthat::test_file("tests/testthat/test-validation.R")

# Watch mode
testthat::auto_test_package()

# Verbose output
devtools::test(reporter = "progress")

# Find slow tests
devtools::test(reporter = "slow")

# Test independence
devtools::test(shuffle = TRUE)

# Full package check
devtools::check()