diff --git a/CHANGELOG.md b/CHANGELOG.md
index e4979a3f..f46f1042 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -160,7 +160,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [0.4.0] - 2020-11-21
 ### Added
 - `arduino_ci_remote.rb` CLI switch `--skip-examples-compilation`
-- Add support for `diditalPinToPort()`, `digitalPinToBitMask()`, `portOutputRegister()`, and `portInputRegister()`
+- Add support for `digitalPinToPort()`, `digitalPinToBitMask()`, `portOutputRegister()`, and `portInputRegister()`
 - `CppLibrary.header_files` to find header files
 - `LibraryProperties` to read metadata from Arduino libraries
 - `CppLibrary.library_properties_path`, `CppLibrary.library_properties?`, `CppLibrary.library_properties` to expose library properties of a Cpp library
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ae677bd1..317cf257 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -13,14 +13,21 @@ Pull requests will trigger a CI job.  The following two commands will be expecte
 
 * `bundle exec rubocop -D .` - code style tests
 * `bundle exec rspec` - functional tests
+* `bundle exec rspec spec/some_file_spec.rb` - functional tests for just some file
 
  If you do not already have a working ruby development environment set up, run the following commands:
 
 ```shell
+# One of the following
 apt-get install ruby ruby-dev    # For Debian/Ubuntu
-dnf install ruby ruby-devel      # For Fedora
-yum install ruby ruby-devel      # For Centos/RHEL
+dnf install ruby ruby-devel      # For Fedora/newer Centos/RHEL
+yum install ruby ruby-devel      # For older Centos/RHEL
+
+# All below
 gem install bundler
+gem install rspec
+# Now you are ready to install dependencies with bundle (as described in the
+# README file) and to run unit tests.
 ```
 
 Be prepared to write tests to accompany any code you would like to see merged.