diff --git a/spec/shell_spec.rb b/spec/shell_spec.rb
new file mode 100644
index 000000000..8d44fdce9
--- /dev/null
+++ b/spec/shell_spec.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'tmpdir'
+require 'open3'
+
+describe Solargraph::Shell do
+  let(:shell) { described_class.new }
+
+  describe 'rbs' do
+    let(:api_map) { instance_double(Solargraph::ApiMap) }
+
+    before do
+      allow(shell).to receive(:`)
+      allow(Solargraph::ApiMap).to receive(:load).and_return(api_map)
+      allow(api_map).to receive(:source_maps).and_return(source_maps)
+    end
+
+    context 'without inference' do
+      let(:source_maps) { [] }
+
+      it 'invokes sord' do
+        capture_both do
+          shell.options = { filename: 'foo.rbs' }
+          shell.rbs
+        end
+        expect(shell)
+          .to have_received(:`)
+          .with("sord #{Dir.pwd}/sig/foo.rbs --rbs --no-regenerate")
+      end
+    end
+
+    context 'with inference' do
+      let(:source_maps) { [source_map] }
+      let(:source_map) { instance_double(Solargraph::SourceMap) }
+      let(:pin) do
+        instance_double(Solargraph::Pin::Method,
+                        namespace: 'My::Namespace', path: 'My::Namespace#foo',
+                        visibility: :public,
+                        parameters: [],
+                        scope: :instance,
+                        location: nil,
+                        name: 'foo',
+                        class: Solargraph::Pin::Method,
+                        return_type: Solargraph::ComplexType::UNDEFINED)
+      end
+
+      it 'infers unknown types on pins' do
+        allow(source_map).to receive(:pins).and_return([pin])
+        allow(pin).to receive_messages(typify: Solargraph::ComplexType.parse('String'),
+                                       docstring: YARD::Docstring.new(''))
+        allow(pin).to receive(:code_object).and_return(nil)
+        capture_both do
+          shell.options = { filename: 'foo.rbs', inference: true }
+          shell.rbs
+        end
+        expect(pin).to have_received(:typify)
+      end
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index faba8172e..5112060c7 100755
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -19,3 +19,29 @@ def with_env_var(name, value)
     ENV[name] = old_value  # Restore the old value
   end
 end
+
+def capture_stdout &block
+  original_stdout = $stdout
+  $stdout = StringIO.new
+  begin
+    block.call
+    $stdout.string
+  ensure
+    $stdout = original_stdout
+  end
+end
+
+def capture_both &block
+  original_stdout = $stdout
+  original_stderr = $stderr
+  stringio = StringIO.new
+  $stdout = stringio
+  $stderr = stringio
+  begin
+    block.call
+  ensure
+    $stdout = original_stdout
+    $stderr = original_stderr
+  end
+  stringio.string
+end