🧪 Add unit tests for _safe_fmt in finnhub_scanner

Implement comprehensive unit tests for the `_safe_fmt` utility function
to ensure robust handling of numeric formatting and edge cases.
- Test None values and custom fallbacks
- Test various numeric types (int, float, string)
- Test custom format strings
- Test error handling for invalid types

Co-authored-by: aguzererler <6199053+aguzererler@users.noreply.github.com>

tests/unit/test_finnhub_scanner_utils.py

@@ -0,0 +1,35 @@
+"""Unit tests for utility functions in finnhub_scanner.py."""
+
+from tradingagents.dataflows.finnhub_scanner import _safe_fmt
+
+def test_safe_fmt_none_returns_default_fallback():
+    assert _safe_fmt(None) == "N/A"
+
+def test_safe_fmt_none_returns_custom_fallback():
+    assert _safe_fmt(None, fallback="Missing") == "Missing"
+
+def test_safe_fmt_valid_float_returns_default_format():
+    assert _safe_fmt(123.456) == "$123.46"
+
+def test_safe_fmt_valid_int_returns_default_format():
+    assert _safe_fmt(100) == "$100.00"
+
+def test_safe_fmt_numeric_string_returns_default_format():
+    assert _safe_fmt("45.678") == "$45.68"
+
+def test_safe_fmt_custom_format():
+    assert _safe_fmt(123.456, fmt="{:.3f}") == "123.456"
+
+def test_safe_fmt_non_numeric_string_returns_original_string():
+    # float("abc") raises ValueError, should return "abc"
+    assert _safe_fmt("abc") == "abc"
+
+def test_safe_fmt_unsupported_type_returns_str_representation():
+    # float([]) raises TypeError, should return "[]"
+    assert _safe_fmt([]) == "[]"
+
+def test_safe_fmt_zero_returns_formatted_zero():
+    assert _safe_fmt(0) == "$0.00"
+
+def test_safe_fmt_negative_number():
+    assert _safe_fmt(-1.23) == "$-1.23"