Ruby: add more tests

pkgs/ruby/spec/lib/kernaux/cmdline_spec.rb

@@ -61,6 +61,12 @@ RSpec.describe KernAux, '.cmdline' do
     end
   end
 
+  context 'when there are not too many args' do
+    let(:str) { 'a ' * 256 }
+
+    specify { expect(cmdline).to eq ['a'] * 256 }
+  end
+
   context 'when there are too many args' do
     let(:str) { 'a ' * 257 }
 
@@ -70,6 +76,12 @@ RSpec.describe KernAux, '.cmdline' do
     end
   end
 
+  context 'when args don\'t cause buffer overflow' do
+    let(:str) { 'a' * 4095 }
+
+    specify { expect(cmdline).to eq ['a' * 4095] }
+  end
+
   context 'when args cause buffer overflow' do
     let(:str) { 'a' * 4096 }