test.patch

diff --git a/test.sh b/test.sh
new file mode 100644
index 00000000..23bcf547
--- /dev/null
+++ b/test.sh
@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+set -uo pipefail
+cd /app
+
+MODE="${1:-new}"
+
+case "$MODE" in
+  base)
+    pytest tests  # run existing repo tests
+    ;;
+  new)
+    pytest tests/test_binary_search_duplicates.py
+    ;;
+  *)
+    echo "unknown mode: $MODE (expected base or new)" >&2
+    exit 2
+    ;;
+esac
\ No newline at end of file
diff --git a/tests/test_binary_search_duplicates.py b/tests/test_binary_search_duplicates.py
new file mode 100644
index 00000000..1030c868
--- /dev/null
+++ b/tests/test_binary_search_duplicates.py
@@ -0,0 +1,8 @@
+def test_binary_search_leftmost_duplicate():
+    assert binary_search([1, 2, 2, 2, 3], 2) == 1
+
+def test_binary_search_all_duplicates():
+    assert binary_search([1, 1, 1, 1], 1) == 0
+
+def test_binary_search_not_found():
+    assert binary_search([1, 2, 3], 4) == -1
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