improve validate testing with examples

also simplified structure of test cases and failure logging

README.md

@@ -4,31 +4,7 @@ A suite of straightforward validation functions. You put something in, you get b
 
 ## 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:
+You can use `errors.Is()` to ascertain the type of errors returned by validation functions. This may be helpful to control side effects, particularly if you are using multiple validators or want to change the error message.
-
-## 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
 

all_test.go

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

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 {
+	testCases := map[string]map[string]error{
-		Input string
+		"0123456789abcdef": {"abcd1234": nil, "abcd 1234": ErrDisallowedChars, "ghijklmno": ErrDisallowedChars},
-		C     string
-		Err   error
 	}
 
-	hexRange := "0123456789abcdef"
+	for setup, values := range testCases {
+		testChars := Chars(setup)
 
-	testCases := []TestCase{
+		for input, want := range values {
-		{Input: "abcd1234", C: hexRange},
+			t.Run(input, func(t *testing.T) {
-		{Input: "abcd 1234", C: hexRange, Err: ErrDisallowedChars},
+				got := testChars(input)
-		{Input: "ghijklmno", C: hexRange, Err: ErrDisallowedChars},
-	}
 
-	for n, tc := range testCases {
+				if !errors.Is(got, want) {
-		t.Logf("(%d) Testing %q against %q", n, tc.Input, tc.C)
+					t.Error("got", got)
-
+					t.Error("want", want)
-		f := Chars(tc.C)
+				}
-		err := f(tc.Input)
+			})
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
 		}
 	}
 }
 
 func TestExceptChars(t *testing.T) {
-	type TestCase struct {
+	testCases := map[string]map[string]error{
-		Input string
+		"0123456789abcdef": {"abcd1234": ErrDisallowedChars, "abcd 1234": ErrDisallowedChars, "ghijklmno": nil},
-		C     string
-		Err   error
 	}
 
-	hexRange := "0123456789abcdef"
+	for setup, values := range testCases {
+		testExceptChars := ExceptChars(setup)
 
-	testCases := []TestCase{
+		for input, want := range values {
-		{Input: "abcd1234", C: hexRange, Err: ErrDisallowedChars},
+			t.Run(input, func(t *testing.T) {
-		{Input: "abcd 1234", C: hexRange, Err: ErrDisallowedChars},
+				got := testExceptChars(input)
-		{Input: "ghijklmno", C: hexRange},
-	}
 
-	for n, tc := range testCases {
+				if !errors.Is(got, want) {
-		t.Logf("(%d) Testing %q against %q", n, tc.Input, tc.C)
+					t.Error("got", got)
-
+					t.Error("want", want)
-		f := ExceptChars(tc.C)
+				}
-		err := f(tc.Input)
+			})
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
 		}
 	}
 }

email_test.go

@@ -2,27 +2,45 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
-func TestEmail(t *testing.T) {
+func ExampleEmail() {
-	type TestCase struct {
+	fmt.Println(Email("not an email"))
-		Input string
+	// Output: invalid email address
-		Err   error
+}
-	}
 
-	testCases := []TestCase{
+func FuzzEmail(f *testing.F) {
-		{Input: "test@example.com"},
+	want := ErrInvalidEmail
-		{Input: "testexample.com", Err: ErrInvalidEmail},
-	}
 
-	for n, tc := range testCases {
+	f.Fuzz(func(t *testing.T, input string) {
-		t.Logf("(%d) Testing %q", n, tc.Input)
+		got := Email(input)
 
-		err := Email(tc.Input)
+		if !errors.Is(got, want) {
-
+			t.Error("got", got)
-		if !errors.Is(err, tc.Err) {
+			t.Error("want", want)
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
 		}
+	})
+}
+
+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) {
+func TestEqual(t *testing.T) {
-	type TestCase struct {
+	testCases := map[string]map[string]error{
-		I   int
+		"abc": {"abc": nil, "def": ErrNotEqual.With("abc"), "xyz": ErrNotEqual.With("abc")},
-		C   int
+		"def": {"abc": ErrNotEqual.With("def"), "def": nil, "xyz": ErrNotEqual.With("def")},
-		Err error
+		"xyz": {"abc": ErrNotEqual.With("xyz"), "def": ErrNotEqual.With("xyz"), "xyz": nil},
 	}
 
-	testCases := []TestCase{
+	for setup, values := range testCases {
-		{I: 1, C: 1},
+		testEqual := Equal(setup)
-		{I: 5 ^ 3, C: 5 ^ 3},
-		{I: 10, C: 15, Err: ErrNotEqual},
-	}
 
-	for i, tc := range testCases {
+		for input, want := range values {
-		t.Logf("(%d) Testing %d against %d", i, tc.I, tc.C)
+			t.Run(fmt.Sprintf("%s/%s", setup, input), func(t *testing.T) {
+				got := testEqual(input)
 
-		f := Equal(tc.C)
+				if !errors.Is(got, want) {
-		err := f(tc.I)
+					t.Error("got", got)
-
+					t.Error("want", want)
-		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)
 		}
 	}
 }

error_test.go

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

in_test.go

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

length.go

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

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

size.go

@@ -10,7 +10,7 @@ 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 +20,7 @@ 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 {
+	testCases := map[int]map[int]error{
-		Input []int
+		0:   {0: nil, 1: ErrMustHaveFewerItems.With(0), 2: ErrMustHaveFewerItems.With(0), 10: ErrMustHaveFewerItems.With(0)},
-		L     int
+		1:   {0: nil, 1: nil, 2: ErrMustHaveFewerItems.With(1), 10: ErrMustHaveFewerItems.With(1)},
-		Err   error
+		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{
+	for max, values := range testCases {
-		{Input: []int{1, 2, 3, 4}, L: 8},
+		testMaxSize := MaxSize[int](max)
-		{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 n, tc := range testCases {
+		for l, want := range values {
-		t.Logf("(%d) Testing %q against maximum length of %d", n, tc.Input, tc.L)
+			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)
+				got := testMaxSize(input)
-		err := f(tc.Input)
 
-		if !errors.Is(err, tc.Err) {
+				if !errors.Is(got, want) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }
 
 func TestMinSize(t *testing.T) {
-	type TestCase struct {
+	testCases := map[int]map[int]error{
-		Input []int
+		0:   {0: nil, 1: nil, 2: nil, 10: nil},
-		L     int
+		1:   {0: ErrMustHaveMoreItems.With(1), 1: nil, 2: nil, 10: nil},
-		Err   error
+		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{
+	for min, values := range testCases {
-		{Input: []int{1, 2, 3, 4}, L: 8, Err: ErrMustHaveMoreItems},
+		testMinSize := MinSize[int](min)
-		{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 n, tc := range testCases {
+		for l, want := range values {
-		t.Logf("(%d) Testing %q against minimum length of %d", n, tc.Input, tc.L)
+			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)
+				got := testMinSize(input)
-		err := f(tc.Input)
 
-		if !errors.Is(err, tc.Err) {
+				if !errors.Is(got, want) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+					t.Error("got", got)
+					t.Error("want", want)
+				}
+			})
 		}
 	}
 }

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

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 {
+	testCases := map[string]error{
-		Input string
+		"00000000-0000-0000-0000-000000000000": nil,
-		Err   error
+		"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{
+	for input, want := range testCases {
-		{Input: "00000000-0000-0000-0000-000000000000"},
+		t.Run(input, func(t *testing.T) {
-		{Input: "01234567-89ab-cdef-0123-456789abcdef"},
+			got := UUID(input)
-		{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 n, tc := range testCases {
+			if !errors.Is(got, want) {
-		t.Logf("(%d) Testing %q", n, tc.Input)
+				t.Error("got", got)
-
+				t.Error("want", want)
-		err := UUID(tc.Input)
+			}
-
+		})
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
-		}
 	}
 }