Fix tiny bug in double 2 string formatting

- I forgot to handle the trailing dots when I added the fmt variant
- UIDouble2Str (the original) lacked the comma check
- Add unit test lol

common/eda_units.cpp

@@ -152,6 +152,13 @@ std::string EDA_UNIT_UTILS::FormatInternalUnits( const EDA_IU_SCALE& aIuScale, i
         {
             buf.pop_back();
         }
+
+        // if the value was really small
+        // we may have just stripped all the zeros after the decimal
+        if( buf[buf.size() - 1] == '.' )
+        {
+            buf.pop_back();
+        }
     }
     else
     {

common/string_utils.cpp

@@ -1104,11 +1104,18 @@ std::string FormatDouble2Str( double aValue )
     {
         buf = fmt::format( "{:.16f}", aValue );
 
-        // remove trailing zeros
+        // remove trailing zeros (and the decimal marker if needed)
         while( !buf.empty() && buf[buf.size() - 1] == '0' )
         {
             buf.pop_back();
         }
+
+        // if the value was really small
+        // we may have just stripped all the zeros after the decimal
+        if( buf[buf.size() - 1] == '.' )
+        {
+            buf.pop_back();
+        }
     }
     else
     {
@@ -1133,7 +1140,7 @@ std::string UIDouble2Str( double aValue )
         while( --len > 0 && buf[len] == '0' )
             buf[len] = '\0';
 
-        if( buf[len] == '.' )
+        if( buf[len] == '.' || buf[len] == ',' )
             buf[len] = '\0';
         else
             ++len;

qa/unittests/common/test_kicad_string.cpp

@@ -36,6 +36,7 @@
  */
 BOOST_AUTO_TEST_SUITE( KicadString )
 
+
 /**
  * Test the #GetTrailingInt method.
  */
@@ -58,6 +59,7 @@ BOOST_AUTO_TEST_CASE( TrailingInt )
     }
 }
 
+
 /**
  * Test the #StrNumCmp method.
  */
@@ -113,4 +115,30 @@ BOOST_AUTO_TEST_CASE( NaturalNumberCompare )
     }
 }
 
+
+/**
+ * Test the #GetTrailingInt method.
+ */
+BOOST_AUTO_TEST_CASE( Double2Str )
+{
+    using CASE = std::pair<double, std::string>;
+
+    // conceptually a little quirky because doubles do have all those pesky additional values
+    const std::vector<CASE> cases = {
+        { 0, "0" },
+        { 1.000, "1" },
+        { 1.050, "1.05" },                       // single trailing zero
+        { 0.00001523, "0.00001523" },            // value less than the magic 0.0001 threshold
+        { 0.00000000000000001523, "0" },         // really small decimal that gets cut off
+        { 623523, "623523" },                    // large whole number
+    };
+
+    for( const auto& c : cases )
+    {
+        // Test both of these functions that work the same but the innards are different
+        BOOST_CHECK_EQUAL( FormatDouble2Str( c.first ), c.second );
+        BOOST_CHECK_EQUAL( UIDouble2Str( c.first ), c.second );
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()