Add test selector runner

.gitignore

@@ -1,2 +1,3 @@
 /target
-/book/build
+/book/build
+Gemfile.lock

Gemfile

@@ -0,0 +1,3 @@
+source "https://rubygems.org"
+
+gem "tomlrb"

run_tests.rb

@@ -0,0 +1,27 @@
+require 'tomlrb'
+
+# Helper functions
+def ensure_build
+    system "cargo build --release"
+    if $?.exitstatus != 0
+        puts "Oops, we could not build the project!"
+        exit 1
+    end
+end
+
+def select_stage
+    toml_data = Tomlrb.load_file('Course.toml')
+    return toml_data['test']['level']
+end
+
+# Build the project
+puts "Building the project..."
+ensure_build
+
+# Run the tests
+puts "Running tests..."
+stage = select_stage
+system "cargo test --release --features stage#{stage}"
+
+# Congrats!
+puts "All Done!"

tests/stage4.rs

@@ -2,7 +2,6 @@
 
 mod helpers;
 
-use helpers::{split_ls_column_output, split_ls_output_by_newline};
 use rstest::rstest;
 use std::process::Command;