Add validator lib

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/validator/validator_custom_test.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package validator
+
+import (
+	"testing"
+)
+
+func TestCustom(t *testing.T) {
+	validator := Custom(ErrorCodeCustom, "value must be positive", func(value any) bool {
+		if num, ok := value.(int); ok {
+			return num > 0
+		}
+		return false
+	})
+
+	tests := []struct {
+		name      string
+		value     any
+		wantError bool
+	}{
+		{"valid positive", 5, false},
+		{"invalid zero", 0, true},
+		{"invalid negative", -5, true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validator(tt.value)
+			if (err != nil) != tt.wantError {
+				t.Errorf("Custom() error = %v, wantError %v", err, tt.wantError)
+			}
+		})
+	}
+}