feat(bookstack-api-vl3): add unit tests for error types and APIError

Test APIError.Error() formatting, status code to sentinel error mapping
via Is(), and error matching through fmt.Errorf wrapping.

errors_test.go

@@ -0,0 +1,63 @@
+package bookstack
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestAPIError_Error(t *testing.T) {
+	tests := []struct {
+		name string
+		err  APIError
+		want string
+	}{
+		{
+			name: "with code",
+			err:  APIError{StatusCode: 404, Code: "not_found", Message: "Page not found"},
+			want: "bookstack API error (status 404, code not_found): Page not found",
+		},
+		{
+			name: "without code",
+			err:  APIError{StatusCode: 500, Message: "Internal error"},
+			want: "bookstack API error (status 500): Internal error",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.err.Error(); got != tt.want {
+				t.Errorf("Error() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestAPIError_Is(t *testing.T) {
+	tests := []struct {
+		status int
+		target error
+		want   bool
+	}{
+		{400, ErrBadRequest, true},
+		{401, ErrUnauthorized, true},
+		{403, ErrForbidden, true},
+		{404, ErrNotFound, true},
+		{429, ErrRateLimited, true},
+		{500, ErrNotFound, false},
+		{200, ErrBadRequest, false},
+	}
+	for _, tt := range tests {
+		apiErr := &APIError{StatusCode: tt.status}
+		if got := errors.Is(apiErr, tt.target); got != tt.want {
+			t.Errorf("errors.Is(APIError{%d}, %v) = %v, want %v", tt.status, tt.target, got, tt.want)
+		}
+	}
+}
+
+func TestAPIError_Is_Wrapped(t *testing.T) {
+	inner := &APIError{StatusCode: 404, Message: "not found"}
+	wrapped := fmt.Errorf("fetching page: %w", inner)
+	if !errors.Is(wrapped, ErrNotFound) {
+		t.Error("expected errors.Is to match ErrNotFound through wrapping")
+	}
+}