tests,stdlib,python: Add tests for base 10 to 2 SI unit check

**Note**: Erin needs to complete the commit by expanding this test to
properly test the behavior of this change.

To run the pyunit tests:

```sh
scons build/ALL/gem5.opt -j`nproc`
./build/ALL/gem5.opt tests/run_pyunit.py
```

Change-Id: I8cea0fe8b088e03e84072a000444953768bc3151

src/python/m5/util/convert.py

@@ -44,6 +44,8 @@
 # from . import warn
 
 # metric prefixes
+from typing import Optional
+
 atto = 1.0e-18
 femto = 1.0e-15
 pico = 1.0e-12
@@ -299,15 +301,29 @@ def toMemoryBandwidth(value):
     return toBinaryFloat(value, "memory bandwidth", "B/s")
 
 
+def _base_10_to_2(value: str) -> Optional[str]:
+    """Convert a base 10 memory/cache size SI prefix strings to base 2. Used
+    in `checkBaseConversion` to provide a warning message to the user. Will
+    return None if no conversion is required.
+
+
+    This function is intentionally separate from `checkBaseConversion` to aid
+    in testing."""
+    size, prefix = _split_suffix_by_prefix(value)
+    if prefix in base_10_to_2.keys():
+        return f"{size}{base_10_to_2[prefix]}"
+    return None
+
+
 def checkBaseConversion(value, unit):
     if type(value) is str:
-        size, prefix = _split_suffix_by_prefix(value)
-        if prefix in base_10_to_2.keys():
+        new_value = _base_10_to_2(value)
+        if new_value:
             from m5.util import warn
 
             warn(
                 f"Base 10 memory/cache size {value} will be cast to base 2"
-                + f" size {size}{base_10_to_2[prefix]}{unit}."
+                + f" size {new_value}{unit}."
             )
 
 

tests/pyunit/util/pyunit_convert_check.py

@@ -277,3 +277,11 @@ class ConvertTestSuite(unittest.TestCase):
         self.assertRaises(ValueError, conv, "-1K")
 
         self.assertEqual(conv("32F"), 273.15)
+
+    def test_base_10_to_2(self):
+        conv = convert._base_10_to_2
+
+        self.assertEqual(conv("1k"), "1Ki")
+        self.assertIsNone(conv("1Ki"))
+
+        # Leaving the rest of this test for Erin to finish.