add simpler test case as per review comment

tests/reused_shape_2_picosvg.ttx

@@ -0,0 +1,53 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ttFont sfntVersion="\x00\x01\x00\x00">
+
+  <GlyphOrder>
+    <!-- The 'id' attribute is only for humans; it is ignored when parsed. -->
+    <GlyphID id="0" name=".notdef"/>
+    <GlyphID id="1" name=".space"/>
+    <GlyphID id="2" name="e000"/>
+  </GlyphOrder>
+
+  <hmtx>
+    <mtx name=".notdef" width="0" lsb="0"/>
+    <mtx name=".space" width="100" lsb="0"/>
+    <mtx name="e000" width="100" lsb="0"/>
+  </hmtx>
+
+  <cmap>
+    <tableVersion version="0"/>
+    <cmap_format_4 platformID="0" platEncID="3" language="0">
+      <map code="0x20" name=".space"/><!-- SPACE -->
+      <map code="0xe000" name="e000"/><!-- ???? -->
+    </cmap_format_4>
+    <cmap_format_4 platformID="3" platEncID="1" language="0">
+      <map code="0x20" name=".space"/><!-- SPACE -->
+      <map code="0xe000" name="e000"/><!-- ???? -->
+    </cmap_format_4>
+  </cmap>
+
+  <loca>
+    <!-- The 'loca' table will be calculated by the compiler -->
+  </loca>
+
+  <glyf>
+
+    <!-- The xMin, yMin, xMax and yMax values
+         will be recalculated by the compiler. -->
+
+    <TTGlyph name=".notdef"/><!-- contains no outline data -->
+
+    <TTGlyph name=".space"/><!-- contains no outline data -->
+
+    <TTGlyph name="e000"/><!-- contains no outline data -->
+
+  </glyf>
+
+  <SVG>
+
+    <svgDoc endGlyphID="2" startGlyphID="2">
+      <![CDATA[<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1"><defs/><g id="glyph2" transform="matrix(0.5 0 0 0.5 0 -100)"><path d="M200,100 A100 100 0 1 1 0,100 A100 100 0 1 1 200,100 Z" fill="#F49924"/><path d="M74.545,71.818 A15 21.818 0 1 1 44.545,71.818 A15 21.818 0 1 1 74.545,71.818 Z" fill="#7E4418" id="glyph2::1"/><use xlink:href="#glyph2::1" x="80.91"/></g></svg>]]>
+    </svgDoc>
+  </SVG>
+
+</ttFont>

tests/write_font_test.py

@@ -217,6 +217,13 @@ def test_vertical_metrics(ascender, descender, linegap):
                 "width": 120,
             },
         ),
+        # Check that we use xlink:href to reuse shapes with <use> elements
+        # https://github.com/googlefonts/nanoemoji/issues/266
+        (
+            ("reused_shape_2.svg",),
+            "reused_shape_2_picosvg.ttx",
+            {"color_format": "picosvg"},
+        ),
     ],
 )
 def test_write_font_binary(svgs, expected_ttx, config_overrides):