fix: unit symbol text output unit tests fixed

src/core/include/units/bits/unit_text.h

@@ -26,6 +26,7 @@
 #include <units/bits/external/text_tools.h>
 #include <units/derived_dimension.h>
 #include <units/prefix.h>
+#include <units/unit.h>
 
 namespace units::detail {
 
@@ -57,7 +58,7 @@ constexpr auto ratio_text()
   }
 }
 
-template<ratio R, std::size_t SymbolLen>
+template<Unit U, ratio R, std::size_t SymbolLen>
 constexpr auto prefix_or_ratio_text()
 {
   if constexpr (R.num == 1 && R.den == 1 && R.exp == 0) {
@@ -67,7 +68,7 @@ constexpr auto prefix_or_ratio_text()
     // try to form a prefix
     using prefix = downcast<detail::prefix_base<R>>;
 
-    if constexpr (!is_same_v<prefix, prefix_base<R>>) {
+    if constexpr (can_be_prefixed<U> && !is_same_v<prefix, prefix_base<R>>) {
       // print as a prefixed unit
       return prefix::symbol;
     } else {
@@ -138,19 +139,16 @@ constexpr auto unit_text()
     // print as a prefix or ratio of a coherent unit
     using coherent_unit = dimension_unit<Dim>;
 
-    if constexpr (has_symbol<coherent_unit>) {
-      // use predefined coherent unit symbol
-      constexpr auto symbol_text = coherent_unit::symbol;
-      constexpr auto prefix_txt =
-        prefix_or_ratio_text<U::ratio / coherent_unit::ratio, symbol_text.standard().size()>();
-      return prefix_txt + symbol_text;
-    } else {
-      // use derived dimension ingredients to create a unit symbol
-      constexpr auto symbol_text = derived_dimension_unit_text<Dim>();
-      constexpr auto prefix_txt =
-        prefix_or_ratio_text<U::ratio / coherent_unit::ratio, symbol_text.standard().size()>();
-      return prefix_txt + symbol_text;
-    }
+    constexpr auto symbol_text = []() {
+      if constexpr (has_symbol<coherent_unit>)
+        return coherent_unit::symbol;
+      else
+        return derived_dimension_unit_text<Dim>();
+    }();
+
+    constexpr auto prefix_txt =
+      prefix_or_ratio_text<U, U::ratio / coherent_unit::ratio, symbol_text.standard().size()>();
+    return prefix_txt + symbol_text;
   }
 }
 

src/core/include/units/generic/dimensionless.h

@@ -30,7 +30,7 @@
 
 namespace units {
 
-struct one : named_unit<one, ""> {};
+struct one : derived_unit<one> {};
 struct percent : named_scaled_unit<percent, "%", ratio(1, 100), one> {};
 
 /**

src/core/include/units/unit.h

@@ -225,6 +225,9 @@ void can_be_prefixed_impl(const volatile alias_unit<U, Symbol>*);
 template<Unit U>
 inline constexpr bool can_be_prefixed<U> = requires(U * u) { can_be_prefixed_impl(u); };
 
+template<ratio R, typename U>
+inline constexpr bool can_be_prefixed<scaled_unit<R, U>> = can_be_prefixed<typename U::reference>;
+
 }  // namespace detail
 
 }  // namespace units