New conjunct_expecation_linter

DESCRIPTION

@@ -56,6 +56,7 @@ Collate:
     'commas_linter.R'
     'comment_linters.R'
     'comments.R'
+    'conjunct_expectation_linter.R'
     'cyclocomp_linter.R'
     'declared_functions.R'
     'deprecated.R'

NAMESPACE

@@ -21,6 +21,7 @@ export(clear_cache)
 export(closed_curly_linter)
 export(commas_linter)
 export(commented_code_linter)
+export(conjunct_expectation_linter)
 export(cyclocomp_linter)
 export(default_linters)
 export(default_settings)

NEWS.md

@@ -90,6 +90,7 @@ function calls. (#850, #851, @renkun-ken)
    + `expect_type_linter()` Require usage of `expect_type(x, t)` over `expect_equal(typeof(x), t)` and similar
    + `expect_s3_class_linter()` Require usage of `expect_s3_class(x, k)` over `expect_equal(class(x), k)` and similar
    + `expect_s4_class_linter()` Require usage of `expect_s4_class(x, k)` over `expect_true(methods::is(x, k))`
+   + `conjunct_expectation_linter()` Require usage of `expect_true(x); expect_true(y)` over `expect_equal(x && y)` and similar
    + `expect_not_linter()` Require usage of `expect_false(x)` over `expect_true(!x)`, and _vice versa_.
    + `expect_true_false_linter()` Require usage of `expect_true(x)` over `expect_equal(x, TRUE)` and similar
    + `expect_named_linter()` Require usage of `expect_named(x, n)` over `expect_equal(names(x), n)` and similar

R/conjunct_expectation_linter.R

@@ -0,0 +1,42 @@
+#' Force && conditions in expect_true(), expect_false() to be written separately
+#'
+#' For readability of test outputs, testing only one thing per call to
+#'   [testthat::expect_true()] is preferable, i.e.,
+#'   `expect_true(A); expect_true(B)` is better than `expect_true(A && B)`, and
+#'   `expect_false(A); expect_false(B)` is better than `expect_false(A || B)`.
+#'
+#' @evalRd rd_tags("expect_true_false_and_condition_linter")
+#' @seealso [linters] for a complete list of linters available in lintr.
+#' @export
+conjunct_expectation_linter <- function() {
+  Linter(function(source_file) {
+    # need the full file to also catch usages at the top level
+    if (length(source_file$full_parsed_content) == 0L) {
+      return(list())
+    }
+
+    xml <- source_file$full_xml_parsed_content
+
+    xpath <- "//expr[
+      (
+        expr[SYMBOL_FUNCTION_CALL[text() = 'expect_true']]
+        and expr[2][AND2]
+      ) or (
+        expr[SYMBOL_FUNCTION_CALL[text() = 'expect_false']]
+        and expr[2][OR2]
+      )
+    ]"
+
+    bad_expr <- xml2::xml_find_all(xml, xpath)
+
+    return(lapply(bad_expr, gen_conjunct_expectation_lint, source_file))
+  })
+}
+
+gen_conjunct_expectation_lint <- function(expr, source_file) {
+  matched_fun <- xml2::xml_text(xml2::xml_find_first(expr, "expr/SYMBOL_FUNCTION_CALL"))
+  op = if (matched_fun == "expect_true") "&&" else "||"
+  message <- sprintf("Instead of %1$s(A %2$s B), write multiple unit tests like %1$s(A) and %1$s(B)", matched_fun, op)
+  message <- paste(message, "The latter will produce better error messages in the case of failure.")
+  xml_nodes_to_lint(expr, source_file, message, type = "warning", global = TRUE)
+}

inst/lintr/linters.csv

@@ -5,6 +5,7 @@ backport_linter,robustness configurable package_development
 closed_curly_linter,style readability default configurable
 commas_linter,style readability default
 commented_code_linter,style readability best_practices default
+conjunct_expectation_linter,package_development best_practices readability
 cyclocomp_linter,style readability best_practices default configurable
 duplicate_argument_linter,correctness common_mistakes configurable
 equals_na_linter,robustness correctness common_mistakes default

tests/testthat/test-conjunct_expectation_linter.R

@@ -0,0 +1,38 @@
+test_that("conjunct_expectation_linter skips allowed usages", {
+  expect_lint("expect_true(x)", NULL, conjunct_expectation_linter())
+  expect_lint("testthat::expect_false(x, y, z)", NULL, conjunct_expectation_linter())
+
+  # more complicated expression
+  expect_lint("expect_true(x || (y && z))", NULL, conjunct_expectation_linter())
+  # the same by operator precedence, though not obvious a priori
+  expect_lint("expect_true(x || y && z)", NULL, conjunct_expectation_linter())
+  expect_lint("expect_true(x && y || z)", NULL, conjunct_expectation_linter())
+})
+
+test_that("conjunct_expectation_linter blocks && conditions with expect_true()", {
+  expect_lint(
+    "expect_true(x && y)",
+    rex::rex("Instead of expect_true(A && B), write multiple unit tests"),
+    conjunct_expectation_linter()
+  )
+
+  expect_lint(
+    "expect_true(x && y && z)",
+    rex::rex("Instead of expect_true(A && B), write multiple unit tests"),
+    conjunct_expectation_linter()
+  )
+})
+
+test_that("conjunct_expectation_linter blocks || conditions with expect_false()", {
+  expect_lint(
+    "expect_false(x || y)",
+    rex::rex("Instead of expect_false(A || B), write multiple unit tests"),
+    conjunct_expectation_linter()
+  )
+
+  expect_lint(
+    "expect_false(x || y || z)",
+    rex::rex("Instead of expect_false(A || B), write multiple unit tests"),
+    conjunct_expectation_linter()
+  )
+})