tests: Add unit tests for utils.py

Added test cases for _parse_size and sha256sum.

tests/utils/misc.py

 from buildstream import utils
+from ..testutils import mock_os
 
+import os
 import pytest
+from contextlib import contextmanager
 
-
-KB = 1024
-MB = (KB * 1024)
-GB = (MB * 1024)
-TB = (GB * 1024)
+KiB = 1024
+MiB = (KiB * 1024)
+GiB = (MiB * 1024)
+TiB = (GiB * 1024)
 
 
 @pytest.mark.parametrize("args, output", [
-    ((KB - 1, 2), "1023B"),
-    ((MB, 2), "1M"),
-    ((KB, 2), "1K"),
-    ((GB, 2), "1G"),
-    ((MB + (MB * 0.1), 2), "1.1M"),
-    ((KB + (KB * 0.152), 2), "1.15K"),
-    ((GB * 1023, 2), "1023G"),
-    ((GB * 1025, 0), "1T"),
-    ((TB * 1025, 2), "1025T"),
+    ((KiB - 1, 2), "1023B"),
+    ((MiB, 2), "1M"),
+    ((KiB, 2), "1K"),
+    ((GiB, 2), "1G"),
+    ((MiB + (MiB * 0.1), 2), "1.1M"),
+    ((KiB + (KiB * 0.152), 2), "1.15K"),
+    ((GiB * 1023, 2), "1023G"),
+    ((GiB * 1025, 0), "1T"),
+    ((TiB * 1025, 2), "1025T"),
 ])
 def test_pretty_size(args, output):
     assert utils._pretty_size(*args) == output
+
+
+@pytest.mark.parametrize("input_, output", [
+    ("abcdefgh", "9c56cc51b374c3ba189210d5b6d4bf57790d351c96c47c02190ecf1e430635ab"),
+    ("123123123213213213", "fb7841aecde5c99ab5c2e1287377fa33e0f647f129a7876b9349f632263b9277"),
+    ("{}!£!£<>}", "b564e0b71213d377dd0bfdf0654186a92649657892cd2cdf3aa7aaac18d917dd"),
+])
+def test_sha256sum(tmpdir, input_, output):
+    dir_ = str(tmpdir)
+    file_ = os.path.join(dir_, "file")
+    with open(file_, "w") as f:
+        f.write(input_)
+
+    sha265sum = utils.sha256sum(file_)
+    assert sha265sum == output, "sha256sum output varies from the expected output."
+
+
+@pytest.mark.parametrize("input_, output", [
+    ("102341", 102341),
+    ("2K", KiB * 2),
+    ("1024M", MiB * 1024),
+    ("10G", GiB * 10),
+    ("1T", TiB),
+])
+def test_parse_size(input_, output):
+    assert utils._parse_size(input_, None) == output, "_parse_size() output varies from the expected output."
+
+
+@pytest.mark.parametrize("size_disk, percent", [
+    (GiB * 100, 50),
+    (GiB * 100, 37),
+    (GiB * 12, 78),
+    (TiB * 12, 78),
+    (MiB * 2, 12),
+])
+def test_parse_size_percent(size_disk, percent):
+    BLOCK_SIZE = 4096
+    expected_output = size_disk * (percent / 100)
+    f_blocks = size_disk / BLOCK_SIZE
+    patched_statvfs = mock_os.mock_statvfs(f_blocks=f_blocks, f_bsize=BLOCK_SIZE)
+
+    with mock_os.monkey_patch("statvfs", patched_statvfs):
+        size = utils._parse_size("{}%".format(percent), None)
+        assert size == expected_output, "_parse_size() output varies from the expected output."