Use counterfeiter for fakes

Author: BooleanCat

CONTRIBUTING.md

@@ -6,16 +6,8 @@ submit changes. Contributions can be made in the form of GitHub
 [pull requests](https://github.com/BooleanCat/go-functional/pulls).
 
 When submitting an issue, please choose the relevant template or choose a blank issue if your query
-doesn't naturally fit into an existing template.
-
-## TL;DR contribution checklist
-
-- [ ] My code is formatted (`make check`)
-- [ ] I have run tests (`make test`)
-- [ ] My code has no lint errors (`make lint`)
-- [ ] All commits in my PR conform to the commit hygiene section
-- [ ] I have added relevant tests
-- [ ] I have not added any dependencies
+doesn't naturally fit into an existing template. The pull request template contains a contribution
+checklist.
 
 ## Zero-dependency
 
@@ -25,6 +17,13 @@ must only incur one dependency: go-functional.
 Development dependencies are OK as they will not be included as dependencies to end-users (such as
 `golangci-lint`).
 
+## Development dependencies
+
+1. [golangci-lint](https://github.com/golangci/golangci-lint) is used to lint the project when
+   running `make check`.
+2. [counterfeiter](https://github.com/maxbrunsfeld/counterfeiter) is used to generate new fakes
+   (using `go generate ./...`). Fakes are declared in `internal/fakes/fakes.go`.
+
 ## Commit hygiene
 
 - Commits should contain only a single change

Makefile

@@ -17,4 +17,4 @@ test:
 
 cov: SHELL:=/bin/bash
 cov:
-	$(GO_BINARY) test -race -coverprofile=coverage.txt -covermode=atomic $$( $(GO_BINARY) list ./... | grep -v assert )
+	$(GO_BINARY) test -race -coverprofile=coverage.txt -covermode=atomic $$( $(GO_BINARY) list ./... | grep -v assert | grep -v fakes )

internal/fakes/fakes.go

@@ -0,0 +1,5 @@
+package fakes
+
+//go:generate counterfeiter -generate
+
+//counterfeiter:generate --fake-name Reader -o . io.Reader

internal/fakes/reader.go

@@ -1,12 +1,14 @@
 package it_test
 
 import (
+	"errors"
 	"fmt"
 	"slices"
 	"strings"
 	"testing"
 
 	"github.com/BooleanCat/go-functional/v2/internal/assert"
+	"github.com/BooleanCat/go-functional/v2/internal/fakes"
 	"github.com/BooleanCat/go-functional/v2/it"
 	"github.com/BooleanCat/go-functional/v2/it/op"
 )
@@ -157,11 +159,13 @@ func ExampleTryCollect() {
 func TestTryCollectError(t *testing.T) {
 	t.Parallel()
 
-	text := new(failSecondTime)
-	lines, err := it.TryCollect(it.LinesString(text))
+	reader := new(fakes.Reader)
+	reader.ReadReturns(0, errors.New("read error"))
+
+	lines, err := it.TryCollect(it.LinesString(reader))
 
 	assert.Equal(t, err.Error(), "read error")
-	assert.SliceEqual(t, lines, []string{"o"})
+	assert.Empty[string](t, lines)
 }
 
 func ExampleLen() {
@@ -249,7 +253,10 @@ func TestMustCollectPanic(t *testing.T) {
 		}
 	}()
 
-	it.MustCollect(it.LinesString(new(failSecondTime)))
+	reader := new(fakes.Reader)
+	reader.ReadReturns(0, errors.New("read error"))
+
+	it.MustCollect(it.LinesString(reader))
 }
 
 func ExampleAll() {

it/iter_test.go

@@ -3,11 +3,11 @@ package it_test
 import (
 	"errors"
 	"fmt"
-	"io"
 	"strings"
 	"testing"
 
 	"github.com/BooleanCat/go-functional/v2/internal/assert"
+	"github.com/BooleanCat/go-functional/v2/internal/fakes"
 	"github.com/BooleanCat/go-functional/v2/it"
 )
 
@@ -70,27 +70,6 @@ func TestLinesYieldsFalseWithError(t *testing.T) {
 	})
 }
 
-type failSecondTime struct {
-	count int
-}
-
-func (f *failSecondTime) Read(p []byte) (n int, err error) {
-	if f.count == 0 {
-		f.count++
-		copy(p, []byte("o"))
-		return 1, nil
-	}
-
-	if f.count == 1 {
-		f.count++
-		return 0, errors.New("read error")
-	}
-
-	return 0, io.EOF
-}
-
-var _ io.Reader = new(failSecondTime)
-
 func TestLinesFailsLater(t *testing.T) {
 	t.Parallel()
 
@@ -99,7 +78,11 @@ func TestLinesFailsLater(t *testing.T) {
 		lastErr error
 	)
 
-	for _, err := range it.LinesString(new(failSecondTime)) {
+	reader := new(fakes.Reader)
+	reader.ReadReturnsOnCall(0, 1, nil)
+	reader.ReadReturnsOnCall(1, 0, errors.New("read error"))
+
+	for _, err := range it.LinesString(reader) {
 		count++
 		lastErr = err
 	}