[decimal] Add tests for subtract() of BigDecimal

mojoproject.toml

@@ -31,7 +31,7 @@ test = "magic run package && magic run mojo test tests --filter"
 t = "clear && magic run package && magic run mojo test tests --filter"
 
 # benches
-bench_dec = "magic run package && cd benches/decimal && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"
-bench_bint = "magic run package && cd benches/bigint && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"
-bench_buint = "magic run package && cd benches/biguint && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"
-bench_bdec = "magic run package && cd benches/bigdecimal && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"
+bench_dec = "clear && magic run package && cd benches/decimal && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"
+bench_bint = "clear && magic run package && cd benches/bigint && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"
+bench_buint = "clear && magic run package && cd benches/biguint && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"
+bench_bdec = "clear && magic run package && cd benches/bigdecimal && magic run mojo -I ../ bench.mojo && cd ../.. && magic run clean"

tests/bigdecimal/test_bigdecimal_arithmetics.mojo

@@ -85,10 +85,80 @@ fn test_add() raises:
     testing.assert_equal(failed, 0, "All addition tests should pass")
 
 
+fn test_subtract() raises:
+    """Test BigDecimal subtraction with various test cases."""
+    print("------------------------------------------------------")
+    print("Testing BigDecimal subtraction...")
+
+    # Debug TOML parsing
+    var toml = parse_file(file_path)
+    print("TOML file loaded successfully")
+
+    # Check what root keys are available
+    print("Available root keys:")
+    for key in toml.root.keys():
+        print("  - " + key[])
+
+    # Try to access the specific section
+    try:
+        var section = toml.get_array_of_tables("subtraction_tests")
+        print("Found subtraction_tests with", len(section), "entries")
+    except e:
+        print("Error accessing subtraction_tests:", String(e))
+
+    # Load test cases from TOML file
+    var test_cases = load_test_cases(file_path, "subtraction_tests")
+    print("Loaded", len(test_cases), "test cases for subtraction")
+
+    # Track test results
+    var passed = 0
+    var failed = 0
+
+    # Run all test cases in a loop
+    for i in range(len(test_cases)):
+        var test_case = test_cases[i]
+        var a = BigDecimal(test_case.a)
+        var b = BigDecimal(test_case.b)
+        var expected = BigDecimal(test_case.expected)
+        var result = a - b
+
+        try:
+            # Using String comparison for easier debugging
+            testing.assert_equal(
+                String(result), String(expected), test_case.description
+            )
+            # print("✓ Case", i + 1, ":", test_case.description)
+            passed += 1
+        except e:
+            print(
+                "✗ Case",
+                i + 1,
+                "failed:",
+                test_case.description,
+                "\n  Input:",
+                test_case.a,
+                "-",
+                test_case.b,
+                "\n  Expected:",
+                test_case.expected,
+                "\n  Got:",
+                String(result),
+                "\n  Error:",
+                String(e),
+            )
+            failed += 1
+
+    print("BigDecimal subtraction tests:", passed, "passed,", failed, "failed")
+    testing.assert_equal(failed, 0, "All subtraction tests should pass")
+
+
 fn main() raises:
     print("Running BigDecimal arithmetic tests")
 
     # Run addition tests
     test_add()
 
+    # Run subtraction tests
+    test_subtract()
+
     print("All BigDecimal arithmetic tests passed!")