improve validate testing with examples

also simplified structure of test cases and failure logging

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)
+			}
+		})
 	}
 }