update package name

also simplified structure of test cases and failure logging

.github/workflows/test.yml

@@ -0,0 +1,47 @@
+name: Test
+
+on:
+  pull_request:
+    branches:
+      - develop
+  push:
+    branches:
+      - develop
+
+jobs:
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: ^1.21.0
+
+      - name: Display Go version
+        run: go version
+
+      - name: Install dependencies
+        run: go get
+
+      - name: Run tests
+        run: go test -v
+
+  notify:
+    name: Send Discord workflow notification
+    runs-on: ubuntu-latest
+    needs: test
+    steps:
+      - name: Send notification
+        uses: annybs/action-notify-discord@v1
+        if: ${{ always() }}
+        with:
+          repository: ${{ github.repository }}
+          result: ${{ needs.test.result }}
+          run-id: ${{ github.run_id }}
+          run-number: ${{ github.run_number }}
+          webhook-url: ${{ secrets.DISCORD_WEBHOOK }}
+          workflow: ${{ github.workflow }}

.gitignore

@@ -0,0 +1 @@
+go.sum

LICENSE.md

@@ -0,0 +1,11 @@
+# MIT License
+
+Copyright © 2024 Aneurin Barker Snook a@aneur.in
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+https://mit-license.org/

README.md

@@ -2,34 +2,6 @@
 
 A suite of straightforward validation functions. You put something in, you get back `nil` or an error.
 
-## Error handling
-
-You can use `errors.Is()` to ascertain the type of errors thrown by validation functions. This may be helpful to control side effects, particularly if using multiple validators and returning early (similar to a strongly-typed try-catch). For example:
-
-## Example
-
-```go
-package main
-
-import (
-	"errors"
-	"fmt"
-
-	"github.com/annybs/go/validate"
-)
-
-func main() {
-	v := validate.Equal("a")
-	if err := v("b"); err != nil {
-		if errors.Is(err, validate.ErrNotEqual) {
-			fmt.Println("failed successfully")
-		} else {
-			fmt.Println("failed unsuccessfully")
-		}
-	}
-}
-```
-
 ## License
 
-See [LICENSE.md](../LICENSE.md)
+See [LICENSE.md](./LICENSE.md)

all_test.go

@@ -2,40 +2,43 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
-func TestAll(t *testing.T) {
-	type TestCase[T any] struct {
-		Input T
-		F     func(T) error
-		Err   error
-	}
+func ExampleAll() {
+	testAll := All(MinLength(4), Chars("0123456789abcdef"))
+	fmt.Println(testAll("invalid input"))
+	// Output: contains disallowed characters
+}
 
-	f := All(
+func TestAll(t *testing.T) {
+	testAll := All(
 		MinLength(4),
 		MaxLength(8),
 		Chars("0123456789abcdef"),
 		In("abcd", "abcdef", "12345678"),
 	)
 
-	testCases := []TestCase[string]{
-		{Input: "abcd", F: f},
-		{Input: "abcdef", F: f},
-		{Input: "12345678", F: f},
-		{Input: "abc", F: f, Err: ErrMustBeLonger},
-		{Input: "abcdef012", F: f, Err: ErrMustBeShorter},
-		{Input: "abcdefgh", F: f, Err: ErrDisallowedChars},
-		{Input: "01abcd", F: f, Err: ErrValueNotAllowed},
+	testCases := map[string]error{
+		"abcd":     nil,
+		"abcdef":   nil,
+		"12345678": nil,
+
+		"abc":       ErrMustBeLonger.With(4),
+		"abcdef012": ErrMustBeShorter.With(8),
+		"abcdefgh":  ErrDisallowedChars,
+		"01abcd":    ErrValueNotAllowed,
 	}
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q", n, tc.Input)
+	for input, want := range testCases {
+		t.Run(input, func(t *testing.T) {
+			got := testAll(input)
 
-		err := tc.F(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
-		}
+			if !errors.Is(got, want) {
+				t.Error("got", got)
+				t.Error("want", want)
+			}
+		})
 	}
 }

chars.go

@@ -4,7 +4,6 @@ import (
 	"strings"
 )
 
-// Validation error.
 var (
 	ErrDisallowedChars = NewError("contains disallowed characters")
 )

chars_test.go

@@ -2,59 +2,60 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
+func ExampleChars() {
+	testChars := Chars("0123456789abcdef")
+	fmt.Println(testChars("invalid input"))
+	// Output: contains disallowed characters
+}
+
+func ExampleExceptChars() {
+	testExceptChars := Chars("0123456789abcdef")
+	fmt.Println(testExceptChars("invalid input"))
+	// Output: contains disallowed characters
+}
+
 func TestChars(t *testing.T) {
-	type TestCase struct {
-		Input string
-		C     string
-		Err   error
+	testCases := map[string]map[string]error{
+		"0123456789abcdef": {"abcd1234": nil, "abcd 1234": ErrDisallowedChars, "ghijklmno": ErrDisallowedChars},
 	}
 
-	hexRange := "0123456789abcdef"
+	for setup, values := range testCases {
+		testChars := Chars(setup)
 
-	testCases := []TestCase{
-		{Input: "abcd1234", C: hexRange},
-		{Input: "abcd 1234", C: hexRange, Err: ErrDisallowedChars},
-		{Input: "ghijklmno", C: hexRange, Err: ErrDisallowedChars},
-	}
+		for input, want := range values {
+			t.Run(input, func(t *testing.T) {
+				got := testChars(input)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q against %q", n, tc.Input, tc.C)
-
-		f := Chars(tc.C)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+				if !errors.Is(got, want) {
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }
 
 func TestExceptChars(t *testing.T) {
-	type TestCase struct {
-		Input string
-		C     string
-		Err   error
+	testCases := map[string]map[string]error{
+		"0123456789abcdef": {"abcd1234": ErrDisallowedChars, "abcd 1234": ErrDisallowedChars, "ghijklmno": nil},
 	}
 
-	hexRange := "0123456789abcdef"
+	for setup, values := range testCases {
+		testExceptChars := ExceptChars(setup)
 
-	testCases := []TestCase{
-		{Input: "abcd1234", C: hexRange, Err: ErrDisallowedChars},
-		{Input: "abcd 1234", C: hexRange, Err: ErrDisallowedChars},
-		{Input: "ghijklmno", C: hexRange},
-	}
+		for input, want := range values {
+			t.Run(input, func(t *testing.T) {
+				got := testExceptChars(input)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q against %q", n, tc.Input, tc.C)
-
-		f := ExceptChars(tc.C)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+				if !errors.Is(got, want) {
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }

email.go

@@ -4,7 +4,6 @@ import (
 	"regexp"
 )
 
-// Validation error.
 var (
 	ErrInvalidEmail = NewError("invalid email address")
 )

email_test.go

@@ -2,27 +2,45 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
-func TestEmail(t *testing.T) {
-	type TestCase struct {
-		Input string
-		Err   error
-	}
+func ExampleEmail() {
+	fmt.Println(Email("not an email"))
+	// Output: invalid email address
+}
 
-	testCases := []TestCase{
-		{Input: "test@example.com"},
-		{Input: "testexample.com", Err: ErrInvalidEmail},
-	}
+func FuzzEmail(f *testing.F) {
+	want := ErrInvalidEmail
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q", n, tc.Input)
+	f.Fuzz(func(t *testing.T, input string) {
+		got := Email(input)
 
-		err := Email(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+		if !errors.Is(got, want) {
+			t.Error("got", got)
+			t.Error("want", want)
 		}
+	})
+}
+
+func TestEmail(t *testing.T) {
+	testCases := map[string]error{
+		"test@example.com":                      nil,
+		"firstname.lastname@some-website.co.uk": nil,
+
+		"not an email":    ErrInvalidEmail,
+		"testexample.com": ErrInvalidEmail,
+	}
+
+	for input, want := range testCases {
+		t.Run(input, func(t *testing.T) {
+			got := Email(input)
+
+			if !errors.Is(got, want) {
+				t.Error("got", got)
+				t.Error("want", want)
+			}
+		})
 	}
 }

equal_test.go

@@ -2,55 +2,29 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
-func TestEqualInt(t *testing.T) {
-	type TestCase struct {
-		I   int
-		C   int
-		Err error
+func TestEqual(t *testing.T) {
+	testCases := map[string]map[string]error{
+		"abc": {"abc": nil, "def": ErrNotEqual.With("abc"), "xyz": ErrNotEqual.With("abc")},
+		"def": {"abc": ErrNotEqual.With("def"), "def": nil, "xyz": ErrNotEqual.With("def")},
+		"xyz": {"abc": ErrNotEqual.With("xyz"), "def": ErrNotEqual.With("xyz"), "xyz": nil},
 	}
 
-	testCases := []TestCase{
-		{I: 1, C: 1},
-		{I: 5 ^ 3, C: 5 ^ 3},
-		{I: 10, C: 15, Err: ErrNotEqual},
-	}
+	for setup, values := range testCases {
+		testEqual := Equal(setup)
 
-	for i, tc := range testCases {
-		t.Logf("(%d) Testing %d against %d", i, tc.I, tc.C)
+		for input, want := range values {
+			t.Run(fmt.Sprintf("%s/%s", setup, input), func(t *testing.T) {
+				got := testEqual(input)
 
-		f := Equal(tc.C)
-		err := f(tc.I)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
-		}
-	}
-}
-
-func TestEqualStr(t *testing.T) {
-	type TestCase struct {
-		I   string
-		C   string
-		Err error
-	}
-
-	testCases := []TestCase{
-		{I: "abc", C: "abc"},
-		{I: "def ghi 123", C: "def ghi 123"},
-		{I: "jkl", C: "mno", Err: ErrNotEqual},
-	}
-
-	for i, tc := range testCases {
-		t.Logf("(%d) Testing %s against %s", i, tc.I, tc.C)
-
-		f := Equal(tc.C)
-		err := f(tc.I)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+				if !errors.Is(got, want) {
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }

error_test.go

@@ -2,48 +2,48 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
 func TestErrorIs(t *testing.T) {
 	type TestCase struct {
-		Err    error
-		Target error
-		Is     bool
+		A    error
+		B    error
+		Want bool
 	}
 
 	testCases := []TestCase{
-		// Is any validation error
-		{Err: Err, Target: Err, Is: true},
-		{Err: ErrDisallowedChars, Target: Err, Is: true},
-		{Err: ErrMustBeGreater, Target: Err, Is: true},
+		// Want any validation error
+		{A: Err, B: Err, Want: true},
+		{A: ErrDisallowedChars, B: Err, Want: true},
+		{A: ErrMustBeGreater, B: Err, Want: true},
 
-		// Is specific validation error
-		{Err: ErrDisallowedChars, Target: ErrDisallowedChars, Is: true},
-		{Err: ErrMustBeGreater, Target: ErrMustBeGreater, Is: true},
+		// Want specific validation error
+		{A: ErrDisallowedChars, B: ErrDisallowedChars, Want: true},
+		{A: ErrMustBeGreater, B: ErrMustBeGreater, Want: true},
 
-		// Is not specific validation error
-		{Err: Err, Target: ErrDisallowedChars},
-		{Err: Err, Target: ErrMustBeGreater},
-		{Err: ErrMustBeGreater, Target: ErrDisallowedChars},
-		{Err: ErrDisallowedChars, Target: ErrMustBeGreater},
+		// Want not specific validation error
+		{A: Err, B: ErrDisallowedChars},
+		{A: Err, B: ErrMustBeGreater},
+		{A: ErrMustBeGreater, B: ErrDisallowedChars},
+		{A: ErrDisallowedChars, B: ErrMustBeGreater},
 
-		// Is not any other error
-		{Err: ErrDisallowedChars, Target: errors.New("contains disallowed characters")},
-		{Err: ErrMustBeGreater, Target: errors.New("must be greater than %v")},
+		// Want not any other error
+		{A: ErrDisallowedChars, B: errors.New("contains disallowed characters")},
+		{A: ErrMustBeGreater, B: errors.New("must be greater than %v")},
 	}
 
-	for i, tc := range testCases {
-		t.Logf("(%d) Testing %v against %v", i, tc.Err, tc.Target)
+	for _, testCase := range testCases {
+		a, b, want := testCase.A, testCase.B, testCase.Want
 
-		if errors.Is(tc.Err, tc.Target) {
-			if !tc.Is {
-				t.Errorf("%v should not equal %v", tc.Err, tc.Target)
+		t.Run(fmt.Sprintf("%v/%v", a, b), func(t *testing.T) {
+			got := errors.Is(a, b)
+
+			if got != want {
+				t.Error("got", got)
+				t.Error("want", want)
 			}
-		} else {
-			if tc.Is {
-				t.Errorf("%v should equal %v", tc.Err, tc.Target)
-			}
-		}
+		})
 	}
 }

go.mod

@@ -1,3 +1,3 @@
-module github.com/annybs/go/validate
+module code.aneur.in/go/validate
 
 go 1.21

in.go

@@ -1,6 +1,5 @@
 package validate
 
-// Validation error.
 var (
 	ErrValueNotAllowed = NewError("not allowed")
 )

in_test.go

@@ -2,59 +2,37 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
-func TestInInt(t *testing.T) {
-	type TestCase struct {
-		Input int
-		A     []int
-		Err   error
-	}
-
-	allow := []int{1, 23, 456}
-	testCases := []TestCase{
-		{Input: 1, A: allow},
-		{Input: 23, A: allow},
-		{Input: 456, A: allow},
-		{Input: 789, A: allow, Err: ErrValueNotAllowed},
-	}
-
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %d against %v", n, tc.Input, tc.A)
-
-		f := In(tc.A...)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
-		}
-	}
+func ExampleIn() {
+	testIn := In("abc", "def", "xyz")
+	fmt.Println(testIn("123"))
+	// Output: not allowed
 }
 
-func TestInString(t *testing.T) {
-	type TestCase struct {
-		Input string
-		A     []string
-		Err   error
+func TestIn(t *testing.T) {
+	testIn := In("abc", "def", "xyz")
+
+	testCases := map[string]error{
+		"abc": nil,
+		"def": nil,
+		"xyz": nil,
+
+		"abcd": ErrValueNotAllowed,
+		"123":  ErrValueNotAllowed,
+		"":     ErrValueNotAllowed,
 	}
 
-	allow := []string{"abcd", "ef", "1234"}
-	testCases := []TestCase{
-		{Input: "abcd", A: allow},
-		{Input: "ef", A: allow},
-		{Input: "1234", A: allow},
-		{Input: "5678", A: allow, Err: ErrValueNotAllowed},
-	}
+	for input, want := range testCases {
+		t.Run(input, func(t *testing.T) {
+			got := testIn(input)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q against %v", n, tc.Input, tc.A)
-
-		f := In(tc.A...)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
-		}
+			if !errors.Is(got, want) {
+				t.Error("got", got)
+				t.Error("want", want)
+			}
+		})
 	}
 }

length.go

@@ -1,9 +1,8 @@
 package validate
 
-// Validation error.
 var (
-	ErrMustBeLonger  = NewError("must be at least %d characters")
-	ErrMustBeShorter = NewError("must be no more than %d characters")
+	ErrMustBeLonger  = NewError("must contain at least %d characters")
+	ErrMustBeShorter = NewError("must contain no more than %d characters")
 )
 
 // MaxLength validates the length of a string as being less than or equal to a given maximum.

length_test.go

@@ -2,57 +2,60 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
+func ExampleMaxLength() {
+	testMaxLength := MaxLength(8)
+	fmt.Println(testMaxLength("this string is too long"))
+	// Output: must contain no more than 8 characters
+}
+
+func ExampleMinLength() {
+	testMinLength := MinLength(8)
+	fmt.Println(testMinLength("2short"))
+	// Output: must contain at least 8 characters
+}
+
 func TestMaxLength(t *testing.T) {
-	type TestCase struct {
-		Input string
-		L     int
-		Err   error
+	testCases := map[int]map[string]error{
+		8: {"abcd": nil, "abcdefgh": nil, "abcd efg": nil, "abcdefghi": ErrMustBeShorter.With(8)},
 	}
 
-	testCases := []TestCase{
-		{Input: "abcd", L: 8},
-		{Input: "abcdefgh", L: 8},
-		{Input: "abcd efg", L: 8},
-		{Input: "abcdefghi", L: 8, Err: ErrMustBeShorter},
-	}
+	for setup, values := range testCases {
+		testMaxLength := MaxLength(setup)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q against maximum length of %d", n, tc.Input, tc.L)
+		for input, want := range values {
+			t.Run(fmt.Sprintf("%d/%s", setup, input), func(t *testing.T) {
+				got := testMaxLength(input)
 
-		f := MaxLength(tc.L)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+				if !errors.Is(got, want) {
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }
 
 func TestMinLength(t *testing.T) {
-	type TestCase struct {
-		Input string
-		L     int
-		Err   error
+	testCases := map[int]map[string]error{
+		8: {"abcd": ErrMustBeLonger.With(8), "abcdefgh": nil, "abcd efg": nil, "abcdefghi": nil},
 	}
 
-	testCases := []TestCase{
-		{Input: "abcd", L: 8, Err: ErrMustBeLonger},
-		{Input: "abcdefgh", L: 8},
-		{Input: "abcd efg", L: 8},
-		{Input: "abcdefghi", L: 8},
-	}
+	for setup, values := range testCases {
+		testMinLength := MinLength(setup)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q against minimum length of %d", n, tc.Input, tc.L)
+		for input, want := range values {
+			t.Run(fmt.Sprintf("%d/%s", setup, input), func(t *testing.T) {
+				got := testMinLength(input)
 
-		f := MinLength(tc.L)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+				if !errors.Is(got, want) {
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }

number.go

@@ -1,6 +1,5 @@
 package validate
 
-// Validation error.
 var (
 	ErrMustBeGreater        = NewError("must be greater than %v")
 	ErrMustBeGreaterOrEqual = NewError("must be greater than or equal to %v")

number_test.go

@@ -2,167 +2,174 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
+func ExampleMax() {
+	testMax := Max(10, true)
+	fmt.Println(testMax(10))
+	// Output: must be less than 10
+}
+
+func ExampleMin() {
+	testMin := Min(10, false)
+	fmt.Println(testMin(5))
+	// Output: must be greater than or equal to 10
+}
+
 func TestMax(t *testing.T) {
-	type TestCase struct {
-		Input int
-		N     int
-		Excl  bool
-		Err   error
+	testCases := map[int]map[bool]map[int]error{
+		10: {
+			true:  {0: nil, 1: nil, 2: nil, 10: ErrMustBeLess.With(10), 100: ErrMustBeLess.With(10)},
+			false: {0: nil, 1: nil, 2: nil, 10: nil, 100: ErrMustBeLessOrEqual.With(10)},
+		},
 	}
 
-	testCases := []TestCase{
-		{Input: 10, N: 0, Err: ErrMustBeLessOrEqual},
-		{Input: 10, N: 10},
-		{Input: 10, N: 15},
-		{Input: 10, N: 10, Excl: true, Err: ErrMustBeLess},
-	}
+	for setup, subSetup := range testCases {
+		for excl, values := range subSetup {
+			testMax := Max(setup, excl)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %d against maximum of %d", n, tc.Input, tc.N)
+			for input, want := range values {
+				t.Run(fmt.Sprintf("%d/%v/%d", setup, excl, input), func(t *testing.T) {
+					got := testMax(input)
 
-		f := Max(tc.N, tc.Excl)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					if !errors.Is(got, want) {
+						t.Error("got", got)
+						t.Error("want", want)
+					}
+				})
+			}
 		}
 	}
 }
 
 func TestMaxFloat32(t *testing.T) {
-	type TestCase struct {
-		Input float32
-		N     float32
-		Excl  bool
-		Err   error
+	testCases := map[float32]map[bool]map[float32]error{
+		10: {
+			true:  {0: nil, 1: nil, 2: nil, 10: ErrMustBeLess.With(10), 100: ErrMustBeLess.With(10)},
+			false: {0: nil, 1: nil, 2: nil, 10: nil, 100: ErrMustBeLessOrEqual.With(10)},
+		},
 	}
 
-	testCases := []TestCase{
-		{Input: 10, N: 0, Err: ErrMustBeLessOrEqual},
-		{Input: 10, N: 10},
-		{Input: 10, N: 15},
-		{Input: 10, N: 10, Excl: true, Err: ErrMustBeLess},
-	}
+	for setup, subSetup := range testCases {
+		for excl, values := range subSetup {
+			testMax := MaxFloat32(setup, excl)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %g against maximum of %g", n, tc.Input, tc.N)
+			for input, want := range values {
+				t.Run(fmt.Sprintf("%f/%v/%f", setup, excl, input), func(t *testing.T) {
+					got := testMax(input)
 
-		f := MaxFloat32(tc.N, tc.Excl)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					if !errors.Is(got, want) {
+						t.Error("got", got)
+						t.Error("want", want)
+					}
+				})
+			}
 		}
 	}
 }
 
 func TestMaxFloat64(t *testing.T) {
-	type TestCase struct {
-		Input float64
-		N     float64
-		Excl  bool
-		Err   error
+	testCases := map[float64]map[bool]map[float64]error{
+		10: {
+			true:  {0: nil, 1: nil, 2: nil, 10: ErrMustBeLess.With(10), 100: ErrMustBeLess.With(10)},
+			false: {0: nil, 1: nil, 2: nil, 10: nil, 100: ErrMustBeLessOrEqual.With(10)},
+		},
 	}
 
-	testCases := []TestCase{
-		{Input: 10, N: 0, Err: ErrMustBeLessOrEqual},
-		{Input: 10, N: 10},
-		{Input: 10, N: 15},
-		{Input: 10, N: 10, Excl: true, Err: ErrMustBeLess},
-	}
+	for setup, subSetup := range testCases {
+		for excl, values := range subSetup {
+			testMax := MaxFloat64(setup, excl)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %g against maximum of %g", n, tc.Input, tc.N)
+			for input, want := range values {
+				t.Run(fmt.Sprintf("%f/%v/%f", setup, excl, input), func(t *testing.T) {
+					got := testMax(input)
 
-		f := MaxFloat64(tc.N, tc.Excl)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					if !errors.Is(got, want) {
+						t.Error("got", got)
+						t.Error("want", want)
+					}
+				})
+			}
 		}
 	}
 }
 
 func TestMin(t *testing.T) {
-	type TestCase struct {
-		Input int
-		N     int
-		Excl  bool
-		Err   error
+	testCases := map[int]map[bool]map[int]error{
+		10: {
+			true:  {0: ErrMustBeGreater.With(10), 1: ErrMustBeGreater.With(10), 2: ErrMustBeGreater.With(10), 10: ErrMustBeGreater.With(10), 100: nil},
+			false: {0: ErrMustBeGreaterOrEqual.With(10), 1: ErrMustBeGreaterOrEqual.With(10), 2: ErrMustBeGreaterOrEqual.With(10), 10: nil, 100: nil},
+		},
 	}
 
-	testCases := []TestCase{
-		{Input: 10, N: 0},
-		{Input: 10, N: 10},
-		{Input: 10, N: 15, Err: ErrMustBeGreaterOrEqual},
-		{Input: 10, N: 10, Excl: true, Err: ErrMustBeGreater},
-	}
+	for setup, subSetup := range testCases {
+		for excl, values := range subSetup {
+			testMin := Min(setup, excl)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %d against minimum of %d", n, tc.Input, tc.N)
+			for input, want := range values {
+				t.Run(fmt.Sprintf("%d/%v/%d", setup, excl, input), func(t *testing.T) {
+					got := testMin(input)
 
-		f := Min(tc.N, tc.Excl)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					if !errors.Is(got, want) {
+						t.Error("got", got)
+						t.Error("want", want)
+					}
+				})
+			}
 		}
 	}
 }
 
 func TestMinFloat32(t *testing.T) {
-	type TestCase struct {
-		Input float32
-		N     float32
-		Excl  bool
-		Err   error
+	testCases := map[float32]map[bool]map[float32]error{
+		10: {
+			true:  {0: ErrMustBeGreater.With(10), 1: ErrMustBeGreater.With(10), 2: ErrMustBeGreater.With(10), 10: ErrMustBeGreater.With(10), 100: nil},
+			false: {0: ErrMustBeGreaterOrEqual.With(10), 1: ErrMustBeGreaterOrEqual.With(10), 2: ErrMustBeGreaterOrEqual.With(10), 10: nil, 100: nil},
+		},
 	}
 
-	testCases := []TestCase{
-		{Input: 10, N: 0},
-		{Input: 10, N: 10},
-		{Input: 10, N: 15, Err: ErrMustBeGreaterOrEqual},
-		{Input: 10, N: 10, Excl: true, Err: ErrMustBeGreater},
-	}
+	for setup, subSetup := range testCases {
+		for excl, values := range subSetup {
+			testMin := MinFloat32(setup, excl)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %g against minimum of %g", n, tc.Input, tc.N)
+			for input, want := range values {
+				t.Run(fmt.Sprintf("%f/%v/%f", setup, excl, input), func(t *testing.T) {
+					got := testMin(input)
 
-		f := MinFloat32(tc.N, tc.Excl)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					if !errors.Is(got, want) {
+						t.Error("got", got)
+						t.Error("want", want)
+					}
+				})
+			}
 		}
 	}
 }
 
 func TestMinFloat64(t *testing.T) {
-	type TestCase struct {
-		Input float64
-		N     float64
-		Excl  bool
-		Err   error
+	testCases := map[float64]map[bool]map[float64]error{
+		10: {
+			true:  {0: ErrMustBeGreater.With(10), 1: ErrMustBeGreater.With(10), 2: ErrMustBeGreater.With(10), 10: ErrMustBeGreater.With(10), 100: nil},
+			false: {0: ErrMustBeGreaterOrEqual.With(10), 1: ErrMustBeGreaterOrEqual.With(10), 2: ErrMustBeGreaterOrEqual.With(10), 10: nil, 100: nil},
+		},
 	}
 
-	testCases := []TestCase{
-		{Input: 10, N: 0},
-		{Input: 10, N: 10},
-		{Input: 10, N: 15, Err: ErrMustBeGreaterOrEqual},
-		{Input: 10, N: 10, Excl: true, Err: ErrMustBeGreater},
-	}
+	for setup, subSetup := range testCases {
+		for excl, values := range subSetup {
+			testMin := MinFloat64(setup, excl)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %g against minimum of %g", n, tc.Input, tc.N)
+			for input, want := range values {
+				t.Run(fmt.Sprintf("%f/%v/%f", setup, excl, input), func(t *testing.T) {
+					got := testMin(input)
 
-		f := MinFloat64(tc.N, tc.Excl)
-		err := f(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					if !errors.Is(got, want) {
+						t.Error("got", got)
+						t.Error("want", want)
+					}
+				})
+			}
 		}
 	}
 }

size.go

@@ -1,6 +1,5 @@
 package validate
 
-// Validation error.
 var (
 	ErrMustHaveMoreItems  = NewError("must have at least %d items")
 	ErrMustHaveFewerItems = NewError("must have no more than %d items")
@@ -10,7 +9,7 @@ var (
 func MaxSize[T any](l int) func([]T) error {
 	return func(value []T) error {
 		if len(value) > l {
-			return ErrMustHaveFewerItems
+			return ErrMustHaveFewerItems.With(l)
 		}
 		return nil
 	}
@@ -20,7 +19,7 @@ func MaxSize[T any](l int) func([]T) error {
 func MinSize[T any](l int) func([]T) error {
 	return func(value []T) error {
 		if len(value) < l {
-			return ErrMustHaveMoreItems
+			return ErrMustHaveMoreItems.With(l)
 		}
 		return nil
 	}

size_test.go

@@ -2,55 +2,78 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
+func ExampleMaxSize() {
+	testMaxSize := MaxSize[string](3)
+	fmt.Println(testMaxSize([]string{"abc", "def", "ghi", "jkl"}))
+	// Output: must have no more than 3 items
+}
+
+func ExampleMinSize() {
+	testMaxSize := MinSize[string](3)
+	fmt.Println(testMaxSize([]string{"abc", "def"}))
+	// Output: must have at least 3 items
+}
+
 func TestMaxSize(t *testing.T) {
-	type TestCase struct {
-		Input []int
-		L     int
-		Err   error
+	testCases := map[int]map[int]error{
+		0:   {0: nil, 1: ErrMustHaveFewerItems.With(0), 2: ErrMustHaveFewerItems.With(0), 10: ErrMustHaveFewerItems.With(0)},
+		1:   {0: nil, 1: nil, 2: ErrMustHaveFewerItems.With(1), 10: ErrMustHaveFewerItems.With(1)},
+		2:   {0: nil, 1: nil, 2: nil, 10: ErrMustHaveFewerItems.With(2)},
+		10:  {0: nil, 1: nil, 2: nil, 10: nil},
+		100: {0: nil, 1: nil, 2: nil, 10: nil},
 	}
 
-	testCases := []TestCase{
-		{Input: []int{1, 2, 3, 4}, L: 8},
-		{Input: []int{1, 2, 3, 4, 5, 6, 7, 8}, L: 8},
-		{Input: []int{1, 2, 3, 4, 5, 6, 7, 8, 9}, L: 8, Err: ErrMustHaveFewerItems},
-	}
+	for max, values := range testCases {
+		testMaxSize := MaxSize[int](max)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q against maximum length of %d", n, tc.Input, tc.L)
+		for l, want := range values {
+			t.Run(fmt.Sprintf("%d/%d", max, l), func(t *testing.T) {
+				input := []int{}
+				for i := 0; i < l; i++ {
+					input = append(input, i)
+				}
 
-		f := MaxSize[int](tc.L)
-		err := f(tc.Input)
+				got := testMaxSize(input)
 
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+				if !errors.Is(got, want) {
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }
 
 func TestMinSize(t *testing.T) {
-	type TestCase struct {
-		Input []int
-		L     int
-		Err   error
+	testCases := map[int]map[int]error{
+		0:   {0: nil, 1: nil, 2: nil, 10: nil},
+		1:   {0: ErrMustHaveMoreItems.With(1), 1: nil, 2: nil, 10: nil},
+		2:   {0: ErrMustHaveMoreItems.With(2), 1: ErrMustHaveMoreItems.With(2), 2: nil, 10: nil},
+		10:  {0: ErrMustHaveMoreItems.With(10), 1: ErrMustHaveMoreItems.With(10), 2: ErrMustHaveMoreItems.With(10), 10: nil},
+		100: {0: ErrMustHaveMoreItems.With(100), 1: ErrMustHaveMoreItems.With(100), 2: ErrMustHaveMoreItems.With(100), 10: ErrMustHaveMoreItems.With(100)},
 	}
 
-	testCases := []TestCase{
-		{Input: []int{1, 2, 3, 4}, L: 8, Err: ErrMustHaveMoreItems},
-		{Input: []int{1, 2, 3, 4, 5, 6, 7, 8}, L: 8},
-		{Input: []int{1, 2, 3, 4, 5, 6, 7, 8, 9}, L: 8},
-	}
+	for min, values := range testCases {
+		testMinSize := MinSize[int](min)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q against minimum length of %d", n, tc.Input, tc.L)
+		for l, want := range values {
+			t.Run(fmt.Sprintf("%d/%d", min, l), func(t *testing.T) {
+				input := []int{}
+				for i := 0; i < l; i++ {
+					input = append(input, i)
+				}
 
-		f := MinSize[int](tc.L)
-		err := f(tc.Input)
+				got := testMinSize(input)
 
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+				if !errors.Is(got, want) {
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }

url.go

@@ -2,7 +2,6 @@ package validate
 
 import "net/url"
 
-// Validation error.
 var (
 	ErrInvalidURL Error = NewError("invalid URL")
 )

url_test.go

@@ -2,30 +2,33 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
+func ExampleURL() {
+	fmt.Println(URL("not a url"))
+	// Output: invalid URL
+}
+
 func TestURL(t *testing.T) {
-	type TestCase struct {
-		Input string
-		Err   error
+	testCases := map[string]error{
+		"http://example.com":                    nil,
+		"http://subdomain.example.com":          nil,
+		"http://www.example.com/some-page.html": nil,
+
+		"not a url":     ErrInvalidURL,
+		"subdomain.com": ErrInvalidURL,
 	}
 
-	testCases := []TestCase{
-		{Input: "http://example.com"},
-		{Input: "http://subdomain.example.com"},
-		{Input: "http://www.example.com/some-page.html"},
-		{Input: "subdomain.com", Err: ErrInvalidURL},
-		{Input: "not a url", Err: ErrInvalidURL},
-	}
+	for input, want := range testCases {
+		t.Run(input, func(t *testing.T) {
+			got := URL(input)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q", n, tc.Input)
-
-		err := URL(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
-		}
+			if !errors.Is(got, want) {
+				t.Error("got", got)
+				t.Error("want", want)
+			}
+		})
 	}
 }

uuid.go

@@ -4,7 +4,6 @@ import (
 	"regexp"
 )
 
-// Validation error.
 var (
 	ErrInvalidUUID = NewError("invalid UUID")
 )

uuid_test.go

@@ -2,32 +2,35 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
+func ExampleUUID() {
+	fmt.Println(UUID("not a uuid"))
+	// Output: invalid UUID
+}
+
 func TestUUID(t *testing.T) {
-	type TestCase struct {
-		Input string
-		Err   error
+	testCases := map[string]error{
+		"00000000-0000-0000-0000-000000000000": nil,
+		"01234567-89ab-cdef-0123-456789abcdef": nil,
+		"abcdef01-2345-6789-abcd-ef0123456789": nil,
+
+		"not a uuid":                           ErrInvalidUUID,
+		"00000000-00-0000-0000-00000000000000": ErrInvalidUUID,
+		"00000000000000000000000000000000":     ErrInvalidUUID,
+		"01234567-89ab-cdef-ghij-klmnopqrstuv": ErrInvalidUUID,
 	}
 
-	testCases := []TestCase{
-		{Input: "00000000-0000-0000-0000-000000000000"},
-		{Input: "01234567-89ab-cdef-0123-456789abcdef"},
-		{Input: "abcdef01-2345-6789-abcd-ef0123456789"},
-		{Input: "Not a UUID", Err: ErrInvalidUUID},
-		{Input: "00000000-00-0000-0000-00000000000000", Err: ErrInvalidUUID},
-		{Input: "00000000000000000000000000000000", Err: ErrInvalidUUID},
-		{Input: "01234567-89ab-cdef-ghij-klmnopqrstuv", Err: ErrInvalidUUID},
-	}
+	for input, want := range testCases {
+		t.Run(input, func(t *testing.T) {
+			got := UUID(input)
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q", n, tc.Input)
-
-		err := UUID(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
-		}
+			if !errors.Is(got, want) {
+				t.Error("got", got)
+				t.Error("want", want)
+			}
+		})
 	}
 }