diff --git a/test/fixtures/addition_output.txt b/test/fixtures/addition_output.txt
new file mode 100644
index 0000000..00750ed
--- /dev/null
+++ b/test/fixtures/addition_output.txt
@@ -0,0 +1 @@
+3
diff --git a/test/fixtures/args_sum_output.txt b/test/fixtures/args_sum_output.txt
new file mode 100644
index 0000000..1e8b314
--- /dev/null
+++ b/test/fixtures/args_sum_output.txt
@@ -0,0 +1 @@
+6
diff --git a/test/fixtures/args_sum_trace.json b/test/fixtures/args_sum_trace.json
new file mode 100644
index 0000000..c295992
--- /dev/null
+++ b/test/fixtures/args_sum_trace.json
@@ -0,0 +1,268 @@
+[
+  {
+    "Type": {
+      "kind": 7,
+      "lang_type": "Integer",
+      "specific_info": {
+        "kind": "None"
+      }
+    }
+  },
+  {
+    "Type": {
+      "kind": 9,
+      "lang_type": "String",
+      "specific_info": {
+        "kind": "None"
+      }
+    }
+  },
+  {
+    "Type": {
+      "kind": 12,
+      "lang_type": "Bool",
+      "specific_info": {
+        "kind": "None"
+      }
+    }
+  },
+  {
+    "Type": {
+      "kind": 9,
+      "lang_type": "Symbol",
+      "specific_info": {
+        "kind": "None"
+      }
+    }
+  },
+  {
+    "Type": {
+      "kind": 24,
+      "lang_type": "No type",
+      "specific_info": {
+        "kind": "None"
+      }
+    }
+  },
+  {
+    "Path": ""
+  },
+  {
+    "Function": {
+      "path_id": 0,
+      "line": 1,
+      "name": "<top-level>"
+    }
+  },
+  {
+    "Call": {
+      "function_id": 0,
+      "args": [
+
+      ]
+    }
+  },
+  {
+    "Path": "test/programs/args_sum.rb"
+  },
+  {
+    "Step": {
+      "path_id": 1,
+      "line": 3
+    }
+  },
+  {
+    "Step": {
+      "path_id": 1,
+      "line": 7
+    }
+  },
+  {
+    "Type": {
+      "kind": 0,
+      "lang_type": "Array",
+      "specific_info": {
+        "kind": "None"
+      }
+    }
+  },
+  {
+    "Type": {
+      "kind": 16,
+      "lang_type": "Object",
+      "specific_info": {
+        "kind": "None"
+      }
+    }
+  },
+  {
+    "VariableName": "self"
+  },
+  {
+    "Value": {
+      "variable_id": 0,
+      "value": {
+        "kind": "Raw",
+        "type_id": 6,
+        "r": "main"
+      }
+    }
+  },
+  {
+    "VariableName": "args"
+  },
+  {
+    "Value": {
+      "variable_id": 1,
+      "value": {
+        "kind": "Sequence",
+        "type_id": 5,
+        "elements": [
+          {
+            "kind": "String",
+            "type_id": 1,
+            "text": "1"
+          },
+          {
+            "kind": "String",
+            "type_id": 1,
+            "text": "2"
+          },
+          {
+            "kind": "String",
+            "type_id": 1,
+            "text": "3"
+          }
+        ],
+        "is_slice": false
+      }
+    }
+  },
+  {
+    "Step": {
+      "path_id": 1,
+      "line": 3
+    }
+  },
+  {
+    "Function": {
+      "path_id": 1,
+      "line": 3,
+      "name": "sum_args"
+    }
+  },
+  {
+    "Call": {
+      "function_id": 1,
+      "args": [
+        {
+          "variable_id": 0,
+          "value": {
+            "kind": "Raw",
+            "type_id": 6,
+            "r": "main"
+          }
+        },
+        {
+          "variable_id": 1,
+          "value": {
+            "kind": "Sequence",
+            "type_id": 5,
+            "elements": [
+              {
+                "kind": "String",
+                "type_id": 1,
+                "text": "1"
+              },
+              {
+                "kind": "String",
+                "type_id": 1,
+                "text": "2"
+              },
+              {
+                "kind": "String",
+                "type_id": 1,
+                "text": "3"
+              }
+            ],
+            "is_slice": false
+          }
+        }
+      ]
+    }
+  },
+  {
+    "Step": {
+      "path_id": 1,
+      "line": 4
+    }
+  },
+  {
+    "Value": {
+      "variable_id": 1,
+      "value": {
+        "kind": "Sequence",
+        "type_id": 5,
+        "elements": [
+          {
+            "kind": "String",
+            "type_id": 1,
+            "text": "1"
+          },
+          {
+            "kind": "String",
+            "type_id": 1,
+            "text": "2"
+          },
+          {
+            "kind": "String",
+            "type_id": 1,
+            "text": "3"
+          }
+        ],
+        "is_slice": false
+      }
+    }
+  },
+  {
+    "Step": {
+      "path_id": 1,
+      "line": 5
+    }
+  },
+  {
+    "VariableName": "<return_value>"
+  },
+  {
+    "Value": {
+      "variable_id": 2,
+      "value": {
+        "kind": "Int",
+        "type_id": 0,
+        "i": 6
+      }
+    }
+  },
+  {
+    "Return": {
+      "return_value": {
+        "kind": "Int",
+        "type_id": 0,
+        "i": 6
+      }
+    }
+  },
+  {
+    "Step": {
+      "path_id": 1,
+      "line": 7
+    }
+  },
+  {
+    "Event": {
+      "kind": 0,
+      "content": "6",
+      "metadata": ""
+    }
+  }
+]
diff --git a/test/fixtures/array_sum_output.txt b/test/fixtures/array_sum_output.txt
new file mode 100644
index 0000000..1e8b314
--- /dev/null
+++ b/test/fixtures/array_sum_output.txt
@@ -0,0 +1 @@
+6
diff --git a/test/fixtures/point_representation_output.txt b/test/fixtures/point_representation_output.txt
new file mode 100644
index 0000000..c3bda07
--- /dev/null
+++ b/test/fixtures/point_representation_output.txt
@@ -0,0 +1 @@
+"(3, 4)"
diff --git a/test/programs/args_sum.rb b/test/programs/args_sum.rb
new file mode 100644
index 0000000..16f9e6a
--- /dev/null
+++ b/test/programs/args_sum.rb
@@ -0,0 +1,8 @@
+#!/usr/bin/env ruby
+
+def sum_args(args)
+  args.map(&:to_i).reduce(0, :+)
+end
+
+puts sum_args(ARGV)
+
diff --git a/test/test_tracer.rb b/test/test_tracer.rb
index 6b15259..54396fc 100644
--- a/test/test_tracer.rb
+++ b/test/test_tracer.rb
@@ -1,24 +1,30 @@
 require 'minitest/autorun'
 require 'json'
 require 'fileutils'
+require 'open3'
 
 class TraceTest < Minitest::Test
   TMP_DIR = File.expand_path('tmp', __dir__)
   FIXTURE_DIR = File.expand_path('fixtures', __dir__)
+  PROGRAM_ARGS = {
+    'args_sum' => %w[1 2 3]
+  }
 
   def setup
     FileUtils.mkdir_p(TMP_DIR)
   end
 
-  def run_trace(program_name)
+  def run_trace(program_name, *args)
     base = File.basename(program_name, '.rb')
     Dir.chdir(File.expand_path('..', __dir__)) do
       program = File.join('test', 'programs', program_name)
       out_dir = File.join('test', 'tmp', base)
       FileUtils.mkdir_p(out_dir)
-      system('ruby', 'gems/pure-ruby-tracer/lib/trace.rb', '--out-dir', out_dir, program)
-      raise "trace failed" unless $?.success?
-      JSON.parse(File.read(File.join(out_dir, 'trace.json')))
+      stdout, stderr, status = Open3.capture3('ruby', 'gems/pure-ruby-tracer/lib/trace.rb', '--out-dir', out_dir, program, *args)
+      raise "trace failed: #{stderr}" unless status.success?
+      trace = JSON.parse(File.read(File.join(out_dir, 'trace.json')))
+      program_out = stdout.lines.reject { |l| l.start_with?('call ') || l.start_with?('return') }.join
+      [trace, program_out]
     end
   end
 
@@ -28,10 +34,22 @@ def expected_trace(program_name)
     JSON.parse(File.read(fixture))
   end
 
+  def expected_output(program_name)
+    base = File.basename(program_name, '.rb')
+    fixture = File.join(FIXTURE_DIR, "#{base}_output.txt")
+    File.read(fixture)
+  end
+
+  def program_args(base)
+    PROGRAM_ARGS.fetch(base, [])
+  end
+
   Dir.glob(File.join(FIXTURE_DIR, '*_trace.json')).each do |fixture|
     base = File.basename(fixture, '_trace.json')
     define_method("test_#{base}") do
-      assert_equal expected_trace("#{base}.rb"), run_trace("#{base}.rb")
+      trace, out = run_trace("#{base}.rb", *program_args(base))
+      assert_equal expected_trace("#{base}.rb"), trace
+      assert_equal expected_output("#{base}.rb"), out
     end
   end
 end