The script was looking in the wrong place for the tests.
#! /bin/bash
GTK_BUILDER_TOOL=${GTK_BUILDER_TOOL:-gtk4-builder-tool}
-TEST_DATA_DIR=${TEST_DATA_DIR:-./simplify-data-3to4}
+TEST_DATA_DIR=${G_TEST_SRCDIR:-.}/simplify-data-3to4
TEST_RESULT_DIR=${TEST_RESULT_DIR:-/tmp}
shopt -s nullglob
#! /bin/bash
GTK_BUILDER_TOOL=${GTK_BUILDER_TOOL:-gtk4-builder-tool}
-TEST_DATA_DIR=${TEST_DATA_DIR:-./simplify-data}
+TEST_DATA_DIR=${G_TEST_SRCDIR:-.}/simplify-data
TEST_RESULT_DIR=${TEST_RESULT_DIR:-/tmp}
shopt -s nullglob