Improve testing infrastructure with dynamic discovery and validation (#20)

## Summary

This PR enhances the testing infrastructure with dynamic test discovery, automated validation, and improved error handling.

## Changes

### Testing Infrastructure
- Added `TestSamplesValidity` integration test that validates all test files against their expected output.
- Implemented dynamic test discovery using `filepath.Glob` to automatically find all `.test` files.
- Renamed `benchmark_test.go` to `lambda_test.go` for better naming consistency.
- Consolidated helper functions into a single `runSample` function.
- Replaced all error handling with `assert` for consistent and clear test output.
- Required all `.test` files to have corresponding `.expected` files.

### Iterator Improvements
- Added `Swap` method to iterator for better reduction algorithm.
- Improved reduction algorithm with LIFO-based iterator implementation.

### Build System
- Added `make test` target to run tests without benchmarks.
- Updated Makefile help text to include the new test target.

### Test Cases
- Added new test cases with expected outputs: `church_5^5`, `church_6^6`, `fast_list_2^30`, `list_2^30`.
- Added validation files for all test cases.

## Test plan

- Run tests with expected output validation.
- Run benchmarks to ensure performance is maintained.
- Verify make targets work correctly.

Reviewed-on: #20
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

Makefile

@@ -1,7 +1,7 @@
 BINARY_NAME=lambda
 TEST=simple
 
-.PHONY: help build run profile explain graph docs bench clean
+.PHONY: help build run profile explain graph docs test bench clean
 .DEFAULT_GOAL := help
 .SILENT:
 
@@ -13,6 +13,7 @@ help:
 	echo "  explain  - Build and run with explanation mode and profiling"
 	echo "  graph    - Generate and open CPU profile visualization"
 	echo "  docs     - Start local godoc server on port 6060"
+	echo "  test     - Run tests for all samples"
 	echo "  bench    - Run benchmarks for all samples"
 	echo "  clean    - Remove all build artifacts"
 
@@ -38,6 +39,9 @@ docs:
 	echo ">>> View at 'http://localhost:6060/pkg/git.maximhutz.com/max/lambda/'"
 	go run golang.org/x/tools/cmd/godoc@latest -http=:6060
 
+test:
+	go test -v ./cmd/lambda
+
 bench:
 	go test -bench=. -benchtime=10x -cpu=4 ./cmd/lambda
 

cmd/lambda/benchmark_test.go

@@ -1,70 +0,0 @@
-package main
-
-import (
-	"os"
-	"testing"
-
-	"git.maximhutz.com/max/lambda/internal/config"
-	"git.maximhutz.com/max/lambda/internal/engine"
-	"git.maximhutz.com/max/lambda/pkg/convert"
-	"git.maximhutz.com/max/lambda/pkg/lambda"
-	"git.maximhutz.com/max/lambda/pkg/saccharine"
-)
-
-// Helper function to run a single sample through the lambda interpreter.
-func runSample(samplePath string) error {
-	// Read the sample file.
-	input, err := os.ReadFile(samplePath)
-	if err != nil {
-		return err
-	}
-
-	// Parse code into syntax tree.
-	ast, err := saccharine.Parse(string(input))
-	if err != nil {
-		return err
-	}
-
-	// Compile expression to lambda calculus.
-	compiled := convert.SaccharineToLambda(ast)
-
-	// Create minimal config for benchmarking.
-	cfg := &config.Config{
-		Source:      config.StringSource{Data: ""},
-		Destination: config.StdoutDestination{},
-		Profile:     "",
-		Explanation: false,
-		Statistics:  false,
-		Verbose:     false,
-	}
-
-	// Create and run the engine.
-	process := engine.New(cfg, &compiled)
-	process.Run()
-
-	// Get final result (to ensure it's not optimized away).
-	_ = lambda.Stringify(compiled)
-
-	return nil
-}
-
-// Benchmark all samples using sub-benchmarks.
-func BenchmarkSamples(b *testing.B) {
-	samples := map[string]string{
-		"Church":     "../../tests/church.test",
-		"Fast":       "../../tests/fast.test",
-		"Saccharine": "../../tests/saccharine.test",
-		"Simple":     "../../tests/simple.test",
-		"Thunk":      "../../tests/thunk.test",
-	}
-
-	for name, path := range samples {
-		b.Run(name, func(b *testing.B) {
-			for b.Loop() {
-				if err := runSample(path); err != nil {
-					b.Fatal(err)
-				}
-			}
-		})
-	}
-}

cmd/lambda/lambda_test.go

@@ -0,0 +1,97 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.maximhutz.com/max/lambda/internal/config"
+	"git.maximhutz.com/max/lambda/internal/engine"
+	"git.maximhutz.com/max/lambda/pkg/convert"
+	"git.maximhutz.com/max/lambda/pkg/lambda"
+	"git.maximhutz.com/max/lambda/pkg/saccharine"
+	"github.com/stretchr/testify/assert"
+)
+
+// Helper function to run a single sample through the lambda interpreter.
+func runSample(samplePath string) (string, error) {
+	// Read the sample file.
+	input, err := os.ReadFile(samplePath)
+	if err != nil {
+		return "", err
+	}
+
+	// Parse code into syntax tree.
+	ast, err := saccharine.Parse(string(input))
+	if err != nil {
+		return "", err
+	}
+
+	// Compile expression to lambda calculus.
+	compiled := convert.SaccharineToLambda(ast)
+
+	// Create minimal config for benchmarking.
+	cfg := &config.Config{
+		Source:      config.StringSource{Data: ""},
+		Destination: config.StdoutDestination{},
+		Profile:     "",
+		Explanation: false,
+		Statistics:  false,
+		Verbose:     false,
+	}
+
+	// Create and run the engine.
+	process := engine.New(cfg, &compiled)
+	process.Run()
+
+	return lambda.Stringify(compiled) + "\n", nil
+}
+
+// Test that all samples produce expected output.
+func TestSamplesValidity(t *testing.T) {
+	// Discover all .test files in the tests directory.
+	testFiles, err := filepath.Glob("../../tests/*.test")
+	assert.NoError(t, err, "Failed to read tests directory.")
+	assert.NotEmpty(t, testFiles, "No '*.test' files found in directory.")
+
+	for _, testPath := range testFiles {
+		// Build expected file path.
+		expectedPath := strings.TrimSuffix(testPath, filepath.Ext(testPath)) + ".expected"
+
+		name := strings.TrimSuffix(filepath.Base(testPath), filepath.Ext(testPath))
+
+		t.Run(name, func(t *testing.T) {
+			// Run the sample and capture output.
+			actual, err := runSample(testPath)
+			assert.NoError(t, err, "Failed to run sample.")
+
+			// Read expected output.
+			expectedBytes, err := os.ReadFile(expectedPath)
+			assert.NoError(t, err, "Failed to read expected output.")
+			expected := string(expectedBytes)
+
+			// Compare outputs.
+			assert.Equal(t, expected, actual, "Output does not match expected.")
+		})
+	}
+}
+
+// Benchmark all samples using sub-benchmarks.
+func BenchmarkSamples(b *testing.B) {
+	// Discover all .test files in the tests directory.
+	testFiles, err := filepath.Glob("../../tests/*.test")
+	assert.NoError(b, err, "Failed to read tests directory.")
+	assert.NotEmpty(b, testFiles, "No '*.test' files found in directory.")
+
+	for _, path := range testFiles {
+		name := strings.TrimSuffix(filepath.Base(path), filepath.Ext(path))
+
+		b.Run(name, func(b *testing.B) {
+			for b.Loop() {
+				_, err := runSample(path)
+				assert.NoError(b, err, "Failed to run sample.")
+			}
+		})
+	}
+}

go.mod

@@ -1,3 +1,11 @@
 module git.maximhutz.com/max/lambda
 
 go 1.25.5
+
+require github.com/stretchr/testify v1.11.1
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

go.sum

@@ -0,0 +1,9 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

pkg/lambda/iterator.go

@@ -5,13 +5,15 @@ type Iterator struct {
 }
 
 func NewIterator(expr *Expression) *Iterator {
-	return &Iterator{
+	return &Iterator{[]*Expression{expr}}
-		trace: []*Expression{expr},
+}
-	}
+
+func (i *Iterator) Done() bool {
+	return len(i.trace) == 0
 }
 
 func (i *Iterator) Current() *Expression {
-	if len(i.trace) < 1 {
+	if i.Done() {
 		return nil
 	}
 
@@ -26,6 +28,22 @@ func (i *Iterator) Parent() *Expression {
 	return i.trace[len(i.trace)-2]
 }
 
+func (i *Iterator) Swap(with Expression) {
+	current := i.Current()
+	if current != nil {
+		*current = with
+	}
+}
+
+func (i *Iterator) Back() bool {
+	if i.Done() {
+		return false
+	}
+
+	i.trace = i.trace[:len(i.trace)-1]
+	return true
+}
+
 func (i *Iterator) Next() {
 	switch typed := (*i.Current()).(type) {
 	case *Abstraction:
@@ -48,12 +66,3 @@ func (i *Iterator) Next() {
 		i.trace = []*Expression{}
 	}
 }
-
-func (i *Iterator) Back() bool {
-	if len(i.trace) == 0 {
-		return false
-	}
-
-	i.trace = i.trace[:len(i.trace)-1]
-	return true
-}

pkg/lambda/reduce.go

@@ -1,32 +1,5 @@
 package lambda
 
-import (
-	"git.maximhutz.com/max/lambda/pkg/lifo"
-)
-
-func ReduceOnce(e *Expression) bool {
-	stack := lifo.New(e)
-
-	for !stack.Empty() {
-		top := stack.MustPop()
-
-		switch typed := (*top).(type) {
-		case *Abstraction:
-			stack.Push(&typed.body)
-		case *Application:
-			if fn, fnOk := typed.abstraction.(*Abstraction); fnOk {
-				*top = Substitute(fn.body, fn.parameter, typed.argument)
-				return true
-			}
-
-			stack.Push(&typed.argument)
-			stack.Push(&typed.abstraction)
-		}
-	}
-
-	return false
-}
-
 func IsViable(e *Expression) (*Abstraction, Expression, bool) {
 	if e == nil {
 		return nil, nil, false
@@ -42,18 +15,15 @@ func IsViable(e *Expression) (*Abstraction, Expression, bool) {
 func ReduceAll(e *Expression, step func()) {
 	it := NewIterator(e)
 
-	for it.Current() != nil {
+	for !it.Done() {
-		current := it.Current()
+		if fn, arg, ok := IsViable(it.Current()); !ok {
-
-		if fn, arg, ok := IsViable(current); !ok {
 			it.Next()
 		} else {
-			*current = Substitute(fn.body, fn.parameter, arg)
+			it.Swap(Substitute(fn.body, fn.parameter, arg))
 			step()
 
 			if _, _, ok := IsViable(it.Parent()); ok {
 				it.Back()
-			} else {
 			}
 		}
 	}

pkg/lifo/lifo.go

@@ -1,35 +0,0 @@
-package lifo
-
-import "fmt"
-
-type LIFO[T any] []T
-
-func New[T any](items ...T) *LIFO[T] {
-	l := LIFO[T](items)
-	return &l
-}
-
-func (l *LIFO[T]) Push(item T) {
-	*l = append(*l, item)
-}
-
-func (l *LIFO[T]) Empty() bool {
-	return len(*l) == 0
-}
-
-func (l *LIFO[T]) MustPop() T {
-	var item T
-
-	*l, item = (*l)[:len(*l)-1], (*l)[len(*l)-1]
-	return item
-}
-
-func (l *LIFO[T]) Pop() (T, error) {
-	var item T
-
-	if l.Empty() {
-		return item, fmt.Errorf("stack is exhausted")
-	}
-
-	return l.MustPop(), nil
-}

tests/church_5^5.test

@@ -1,7 +1,8 @@
 0 := \f.\x.x
 inc n := \f x.(f (n f x))
 exp n m := (m n)
+print n := (n F X)
 
 N := (inc (inc (inc (inc (inc 0)))))
 
-(exp N N)
+(print (exp N N))

tests/church_6^6.test

@@ -0,0 +1,8 @@
+0 := \f.\x.x
+inc n := \f x.(f (n f x))
+exp n m := (m n)
+print n := (n F X)
+
+N := (inc (inc (inc (inc (inc (inc 0))))))
+
+(print (exp N N))

tests/fast_list_2^30.expected

@@ -0,0 +1 @@
+(0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (1 END)))))))))))))))))))))))))))))))

tests/list_2^30.expected

@@ -0,0 +1 @@
+(0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (1 END)))))))))))))))))))))))))))))))

tests/simple.test

@@ -1,16 +0,0 @@
-(\0.
-  (\inc.
-    (\add.
-      (\mult.
-        (\exp.
-          (exp (inc (inc (inc (inc 0)))) (inc (inc (inc (inc (inc 0))))))
-          \n m.(m n)
-        )
-        \m n f.(m (n f))
-      )
-      \n m.(m inc n)
-    )
-    \n f x.(f (n f x))
-  )
-  \f x.x
-)

tests/thunk.expected

@@ -0,0 +1 @@
+VALUE