diff --git a/CHANGELOG.md b/CHANGELOG.md
index 64257932..dae3ab9a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 ### Added
 
+- Added support for `ARDUINO_CI_UNIT_TEST_EXTRA_COMPILER_FLAGS` environment variable.
+- Added support for overriding the shell used to execute `CUSTOM_INIT_SCRIPT`
+  by setting `CUSTOM_INIT_SCRIPT_SHELL` (defaults to `/bin/sh`).
+- Added support running scripts before and/or after each run of unit tests with
+  `ARDUINO_CI_PRE_UNIT_TEST_RUN_SCRIPT` and `ARDUINO_CI_POST_UNIT_TEST_RUN_SCRIPT`.
+
 ### Changed
 
 ### Deprecated
diff --git a/REFERENCE.md b/REFERENCE.md
index 7767251e..5e368a93 100644
--- a/REFERENCE.md
+++ b/REFERENCE.md
@@ -51,8 +51,41 @@ This specifies the minimum free SRAM memory for stack/heap, in bytes, that _must
 
 ### `CUSTOM_INIT_SCRIPT` environment variable
 
-If set, testing will execute (using `/bin/sh`) the script referred to by this variable -- relative to the current working directory (i.e. the root directory of the library).  The script will _run_ in the Arduino Libraries directory (changing to the Libraries directory, running the script, and returning to the individual library root afterward).  This enables use cases like the GitHub action to install custom library versions (i.e. a version of a library that is different than what the library manager would automatically install by name) prior to CI test runs.
+If set, testing will execute the script referred to by this variable -- relative
+to the current working directory (i.e. the root directory of the library). By
+default the script will be executed using `/bin/sh` but you can override by
+setting `CUSTOM_INIT_SCRIPT_SHELL` (e.g to `powershell`, `/usr/bin/perl` etc).
+The script will _run_ in the Arduino Libraries directory
+(changing to the Libraries directory, running the script, and returning to the
+individual library root afterward).  This enables use cases like the GitHub
+action to install custom library versions (i.e. a version of a library that
+is different than what the library manager would automatically install by name)
+prior to CI test runs.
+
+### `ARDUINO_CI_PRE_UNIT_TEST_RUN_SCRIPT` and `ARDUINO_CI_POST_UNIT_TEST_RUN_SCRIPT` environment variables
+
+If set, the corresponding script will be run before/after each run of unit tests
+for each configured platform and for each compiler, e.g. if `.arduino-ci.yaml`
+contains
 
+```yaml
+unittest:
+  compilers:
+    - g++-10
+    - g++-11
+  libraries: ~
+  platforms:
+    - leonardo
+    - uno
+```
+
+the scripts will be invoked four times, with the current platform name being
+tested as the first parameter to the script and the current compiler used as
+the second parameter. It is not necessary to define both PRE and POST script;
+if you only want to run something before or after unit tests that's fine.
+By default the scripts are executed by `/bin/sh`, you can override by setting
+`ARDUINO_CI_PRE_UNIT_TEST_RUN_SCRIPT_SHELL` and
+`ARDUINO_CI_POST_UNIT_TEST_RUN_SCRIPT_SHELL` respectively.
 
 ### `USE_SUBDIR` environment variable
 
@@ -68,6 +101,23 @@ If set, testing will fail if no unit test files are detected (or if the director
 
 If set, testing will fail if no example sketches are detected.  This is to avoid communicating a passing status in cases where a commit may have accidentally moved or deleted the examples.
 
+### `ARDUINO_CI_UNIT_TEST_EXTRA_COMPILER_FLAGS` environment variable
+
+If you want to pass on additional flags to the compiler when it runs unit tests
+you can set this variable, e.g.
+
+```bash
+export ARDUINO_CI_UNIT_TEST_EXTRA_COMPILER_FLAGS="--coverage -g -O0"
+```
+
+By default the variable will be split up by space characters. If one of the
+flags contain spaces use the `ARDUINO_CI_TEST_EXTRA_COMPILER_FLAGS_DELIMITER`
+variable to chose a different delimiter, e.g.
+
+```bash
+export ARDUINO_CI_TEST_EXTRA_COMPILER_FLAGS_DELIMITER="|"
+export ARDUINO_CI_UNIT_TEST_EXTRA_COMPILER_FLAGS="-Wall|-DGREETING='Hello world'"
+```
 
 ## Indirectly Overriding Build Behavior (medium term use), and Advanced Options
 
diff --git a/exe/arduino_ci.rb b/exe/arduino_ci.rb
index 72d455ed..c3146aec 100755
--- a/exe/arduino_ci.rb
+++ b/exe/arduino_ci.rb
@@ -15,6 +15,8 @@
 VAR_USE_SUBDIR         = "USE_SUBDIR".freeze
 VAR_EXPECT_EXAMPLES    = "EXPECT_EXAMPLES".freeze
 VAR_EXPECT_UNITTESTS   = "EXPECT_UNITTESTS".freeze
+VAR_ARDUINO_CI_PRE_UNIT_TEST_RUN_SCRIPT  = "ARDUINO_CI_PRE_UNIT_TEST_RUN_SCRIPT".freeze
+VAR_ARDUINO_CI_POST_UNIT_TEST_RUN_SCRIPT = "ARDUINO_CI_POST_UNIT_TEST_RUN_SCRIPT".freeze
 
 @failure_count = 0
 @passfail = proc { |result| result ? "✓" : "✗" }
@@ -66,6 +68,10 @@ def self.parse(options)
         puts "Additionally, the following environment variables control the script:"
         puts " - #{VAR_CUSTOM_INIT_SCRIPT} - if set, this script will be run from the Arduino/libraries directory"
         puts "       prior to any automated library installation or testing (e.g. to install unofficial libraries)"
+        puts " - #{VAR_CUSTOM_INIT_SCRIPT}_SHELL - if set, this will override the"
+        puts "       default shell (/bin/sh) used to execute #{VAR_CUSTOM_INIT_SCRIPT} with."
+        puts " - #{VAR_ARDUINO_CI_PRE_UNIT_TEST_RUN_SCRIPT} and/or #{VAR_ARDUINO_CI_POST_UNIT_TEST_RUN_SCRIPT}"
+        puts "       if set, run the script before/after each unit test run"
         puts " - #{VAR_USE_SUBDIR} - if set, the script will install the library from this subdirectory of the cwd"
         puts " - #{VAR_EXPECT_EXAMPLES} - if set, testing will fail if no example sketches are present"
         puts " - #{VAR_EXPECT_UNITTESTS} - if set, testing will fail if no unit tests are present"
@@ -329,23 +335,24 @@ def get_annotated_compilers(config, cpp_library)
   compilers
 end
 
-# Handle existence or nonexistence of custom initialization script -- run it if you have it
+# Run custom custom script specified by user.
 #
 # This feature is to drive GitHub actions / docker image installation where the container is
 # in a clean-slate state but needs some way to have custom library versions injected into it.
-# In this case, the user provided script would fetch a git repo or some other method
-def perform_custom_initialization(_config)
-  script_path = ENV[VAR_CUSTOM_INIT_SCRIPT]
-  inform("Environment variable #{VAR_CUSTOM_INIT_SCRIPT}") { "'#{script_path}'" }
+# In this case, the user provided script would fetch a git repo or some other method.
+def run_custom_script(env_var, *args)
+  script_path = ENV[env_var]
+  script_shell = ENV[env_var + "_SHELL"] || "/bin/sh"
+  inform("Environment variable #{env_var}") { "'#{script_path}'" }
   return if script_path.nil?
   return if script_path.empty?
 
   script_pathname = Pathname.getwd + script_path
-  assure("Script at #{VAR_CUSTOM_INIT_SCRIPT} exists") { script_pathname.exist? }
+  assure("Script at #{env_var} exists") { script_pathname.exist? }
 
-  assure_multiline("Running #{script_pathname} with sh in libraries working dir") do
+  assure_multiline("Running #{script_pathname} with #{script_shell} in libraries working dir") do
     Dir.chdir(@backend.lib_dir) do
-      IO.popen(["/bin/sh", script_pathname.to_s], err: [:child, :out]) do |io|
+      IO.popen([script_shell, script_pathname.to_s, *args], err: [:child, :out]) do |io|
         io.each_line { |line| puts "    #{line}" }
       end
     end
@@ -441,6 +448,7 @@ def perform_unit_tests(cpp_library, file_config)
   platforms.each do |p|
     puts
     compilers.each do |gcc_binary|
+      run_custom_script(VAR_ARDUINO_CI_PRE_UNIT_TEST_RUN_SCRIPT, p, gcc_binary)
       # before compiling the tests, build a shared library of everything except the test code
       next @failure_count += 1 unless build_shared_library(gcc_binary, p, config, cpp_library)
 
@@ -460,6 +468,7 @@ def perform_unit_tests(cpp_library, file_config)
           cpp_library.run_test_file(exe)
         end
       end
+      run_custom_script(VAR_ARDUINO_CI_POST_UNIT_TEST_RUN_SCRIPT, p, gcc_binary)
     end
   end
 end
@@ -567,7 +576,7 @@ def perform_example_compilation_tests(cpp_library, config)
 end
 
 # run any library init scripts from the library itself.
-perform_custom_initialization(config)
+run_custom_script(VAR_CUSTOM_INIT_SCRIPT)
 
 # initialize library under test
 inform("Environment variable #{VAR_USE_SUBDIR}") { "'#{ENV[VAR_USE_SUBDIR]}'" }
diff --git a/lib/arduino_ci/cpp_library.rb b/lib/arduino_ci/cpp_library.rb
index 8ee111ea..4e5317c2 100644
--- a/lib/arduino_ci/cpp_library.rb
+++ b/lib/arduino_ci/cpp_library.rb
@@ -485,6 +485,18 @@ def test_args(aux_libraries, ci_gcc_config)
       ret
     end
 
+    # Allow users to inject extra compiler flags though environment variable.
+    def extra_compiler_flags_for_unittest
+      return [] unless ENV["ARDUINO_CI_UNIT_TEST_EXTRA_COMPILER_FLAGS"]
+
+      delimiter = if ENV["ARDUINO_CI_TEST_EXTRA_COMPILER_FLAGS_DELIMITER"]
+        yield(ENV["ARDUINO_CI_TEST_EXTRA_COMPILER_FLAGS_DELIMITER"])
+      else
+        " "
+      end
+      ENV["ARDUINO_CI_UNIT_TEST_EXTRA_COMPILER_FLAGS"].split(delimiter)
+    end
+
     # build a file for running a test of the given unit test file
     #
     # The dependent libraries configuration is appended with data from library.properties internal to the library under test
@@ -505,6 +517,7 @@ def build_for_test(test_file, gcc_binary)
         ]
       end
       arg_sets << @test_args
+      arg_sets << extra_compiler_flags_for_unittest
       arg_sets << [test_file.to_s, "-l#{LIBRARY_NAME}"]
       args = arg_sets.flatten(1)
       return nil unless run_gcc(gcc_binary, *args)
@@ -555,6 +568,7 @@ def build_shared_library(aux_libraries, gcc_binary, ci_gcc_config)
       @test_args = test_args(@full_dependencies, ci_gcc_config) # build full set of include directories to be cached for later
 
       arg_sets << @test_args
+      arg_sets << extra_compiler_flags_for_unittest
       arg_sets << cpp_files_arduino.map(&:to_s)  # Arduino.cpp, Godmode.cpp, and stdlib.cpp
       arg_sets << cpp_files_unittest.map(&:to_s) # ArduinoUnitTests.cpp
       arg_sets << cpp_files.map(&:to_s) # CPP files for the primary application library under test