Improve reporting of code not covered by tests (#38)

spec/spec_helper.rb

@@ -21,17 +21,102 @@
 
 SimpleCov.formatters = [SimpleCov::Formatter::HTMLFormatter, SimpleCov::Formatter::LcovFormatter]
 
-# Fail the rspec run if code coverage falls below the configured threshold
+# Return `true` if the environment variable is set to a truthy value
+#
+# @example
+#   env_true?('COV_SHOW_UNCOVERED')
+#
+# @param name [String] the name of the environment variable
+# @return [Boolean]
+#
+def env_true?(name)
+  value = ENV.fetch(name, '').downcase
+  %w[yes on true 1].include?(value)
+end
+
+# Return `true` if the environment variable is NOT set to a truthy value
+#
+# @example
+#   env_false?('COV_NO_FAIL')
+#
+# @param name [String] the name of the environment variable
+# @return [Boolean]
+#
+def env_false?(name)
+  !env_true?(name)
+end
+
+# Return `true` if the the test run should fail if the coverage is below the threshold
+#
+# @return [Boolean]
+#
+def fail_on_low_coverage?
+  !(RSpec.configuration.dry_run? || env_true?('COV_NO_FAIL'))
+end
+
+# Return `true` if the the test run should show the lines not covered by tests
+#
+# @return [Boolean]
+#
+def show_lines_not_covered?
+  env_true?('COV_SHOW_UNCOVERED')
+end
+
+# Report if the test coverage was below the configured threshold
+#
+# The threshold is configured by setting the `test_coverage_threshold` variable
+# in this file.
+#
+# Example:
+#
+# ```Ruby
+# test_coverage_threshold = 100
+# ```
+#
+# Coverage below the threshold will cause the rspec run to fail unless the
+# `COV_NO_FAIL` environment variable is set to TRUE.
+#
+# ```Shell
+# COV_NO_FAIL=TRUE rspec
+# ```
+#
+# Example of running the tests in an infinite loop writing failures to `fail.txt`:
+#
+# ```Shell
+# while true; do COV_NO_FAIL=TRUE rspec >> fail.txt; done
+# ````
+#
+# The lines missing coverage will be displayed if the `COV_SHOW_UNCOVERED`
+# environment variable is set to TRUE.
+#
+# ```Shell
+# COV_SHOW_UNCOVERED=TRUE rspec
+# ```
 #
 test_coverage_threshold = 100
+
 SimpleCov.at_exit do
-  unless RSpec.configuration.dry_run?
-    SimpleCov.result.format!
-    if SimpleCov.result.covered_percent < test_coverage_threshold
-      warn "FAIL: RSpec Test coverage fell below #{test_coverage_threshold}%"
-      exit 1
+  SimpleCov.result.format!
+  # rubocop:disable Style/StderrPuts
+  if SimpleCov.result.covered_percent < test_coverage_threshold
+    $stderr.puts
+    $stderr.print 'FAIL: ' if fail_on_low_coverage?
+    $stderr.puts "RSpec Test coverage fell below #{test_coverage_threshold}%"
+
+    if show_lines_not_covered?
+      $stderr.puts "\nThe following lines were not covered by tests:\n"
+      SimpleCov.result.files.each do |source_file| # SimpleCov::SourceFile
+        source_file.missed_lines.each do |line| # SimpleCov::SourceFile::Line
+          $stderr.puts "  .#{source_file.project_filename}:#{line.number}"
+        end
+      end
     end
+
+    $stderr.puts
+
+    exit 1 if fail_on_low_coverage?
   end
+  # rubocop:enable Style/StderrPuts
 end
 
 SimpleCov.start