run-tests: add option --copy-src

test/lib/copy-src.sh

@@ -0,0 +1,18 @@
+# Re-run run-tests.sh in a snapshot copy of the source.
+# Maintain /tmp/nix-bitcoin-src as a source cache to minimize copies.
+
+tmp=$(mktemp -d '/tmp/nix-bitcoin-src.XXXXX')
+
+# Ignore errors from now on
+set +e
+
+# Move source cache if it exists (atomic)
+mv /tmp/nix-bitcoin-src $tmp/src 2>/dev/null
+
+rsync -a --delete --exclude='.git*' "$scriptDir/../" $tmp/src && \
+  echo "Copied src" && \
+  _nixBitcoinInCopySrc=1 $tmp/src/test/run-tests.sh "${args[@]}"
+
+# Set the current src as the source cache (atomic)
+mv -T $tmp/src /tmp/nix-bitcoin-src 2>/dev/null
+rm -rf $tmp