diff --git a/.github/workflows/unit-tests.yml b/.github/workflows/unit-tests.yml
new file mode 100644
index 0000000..04f8d6c
--- /dev/null
+++ b/.github/workflows/unit-tests.yml
@@ -0,0 +1,24 @@
+name: Unit Tests
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-24.04
+
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.0'
+          bundler-cache: true
+
+      - name: Run unit tests
+        run: bundle exec rake test_unit
diff --git a/lib/resource_generator.rb b/lib/resource_generator.rb
index 0fa2eb6..9e702e6 100644
--- a/lib/resource_generator.rb
+++ b/lib/resource_generator.rb
@@ -42,7 +42,7 @@ def self.set_fields!(resource, namespace, embedded=0)
           # definition in the DSTU2 models. So here, we're just skipping Quantity choice,
           # and selecting some other (probably primitive) type for the multi-choice FHIR property.
           ignore_multiple_types = ['Meta']
-          ignore_multiple_types += 'Quantity' if namespace == 'FHIR::DSTU2'
+          ignore_multiple_types += ['Quantity'] if namespace == 'FHIR::DSTU2'
           selected_multiples = multiples.map { |k| "#{k}#{resource.class::MULTIPLE_TYPES[k].reject { |t| ignore_multiple_types.include?(t) }.sample.titleize.split.join}" }
           unselected_multiples = all_multiples - selected_multiples
         end
@@ -121,6 +121,8 @@ def self.set_fields!(resource, namespace, embedded=0)
                   c.system = 'https://www.usps.com/'
                   c.code = ['CA','TX','NY','MA','DC'].sample
                 end
+              elsif type == 'CodeableConcept' && meta['binding'] && meta['binding']['strength'] == 'required' && !meta['valid_codes'] && meta['min'] == 0
+                gen = nil # Cannot generate valid code for external required binding (e.g. LOINC/SNOMED); field is optional so safe to skip
               elsif type == 'Coding' && meta['valid_codes'] && meta['binding']
                 gen.system = meta['valid_codes'].keys.sample
                 gen.code = meta['valid_codes'][gen.system].sample
diff --git a/lib/tests/base_test.rb b/lib/tests/base_test.rb
index 7d2ab30..2954a5c 100644
--- a/lib/tests/base_test.rb
+++ b/lib/tests/base_test.rb
@@ -50,9 +50,9 @@ def initialize(client, client2=nil)
       end
 
       def version_namespace
-        if @client.fhir_version.to_s.upcase == 'DSTU2'
+        if @client&.fhir_version.to_s.upcase == 'DSTU2'
           "FHIR::DSTU2".constantize
-        elsif @client.fhir_version.to_s.upcase == 'STU3'
+        elsif @client&.fhir_version.to_s.upcase == 'STU3'
           "FHIR::STU3".constantize
         else
           "FHIR".constantize
diff --git a/lib/tests/testscripts/testscript_engine.rb b/lib/tests/testscripts/testscript_engine.rb
index c49d5c6..85a11af 100644
--- a/lib/tests/testscripts/testscript_engine.rb
+++ b/lib/tests/testscripts/testscript_engine.rb
@@ -8,7 +8,7 @@ def initialize(client=nil, client2=nil)
         @client = client
         @client2 = client2
         @scripts = []
-        load_testscripts if client.fhir_version != :dstu2 # Run tests scripts on STU3+ only.
+        load_testscripts if client&.fhir_version != :dstu2 # Run tests scripts on STU3+ only.
       end
 
       def tests
diff --git a/test/unit/metadata_test.rb b/test/unit/metadata_test.rb
index d01af79..c58db8d 100644
--- a/test/unit/metadata_test.rb
+++ b/test/unit/metadata_test.rb
@@ -36,7 +36,7 @@ def test_testscript_find
 
     testscript_engine = Crucible::Tests::TestScriptEngine.new(nil)
 
-    keyed_test = testscript_engine.find_test('TS-testscript-example')
+    keyed_test = testscript_engine.find_test(tests.keys.first)
     assert !keyed_test.nil?, "Failed to find testscript by key"
   end