fix(test): add some tolerance in test_serial_dos

test_serial_dos ensures that the internal FIFO buffer used for storing
the bytes to be written does not grow indefinitely. Some times during
the test we observe small allocations that make the assertion fail.
Add some tolerance to the test (1%) to avoid false positives.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Author: bchalios

tests/integration_tests/functional/test_serial_io.py

@@ -120,7 +120,9 @@ def get_total_mem_size(pid):
     _, stdout, stderr = utils.check_output(cmd)
     assert stderr == ""
 
-    return stdout
+    # This assumes that the pmap returns something in the form of
+    # 123456789K (which is typically the case for us)
+    return float(stdout.strip()[:-1] * 1000)
 
 
 def send_bytes(tty, bytes_count, timeout=60):
@@ -156,7 +158,9 @@ def test_serial_dos(uvm_plain_any):
     before_size = get_total_mem_size(microvm.firecracker_pid)
     send_bytes(tty_fd, 100000000, timeout=1)
     after_size = get_total_mem_size(microvm.firecracker_pid)
-    assert before_size == after_size, (
+    # Give the check a bit of tolerance (1%) since sometimes random unrelated
+    # allocations break it.
+    assert after_size <= (before_size * 1.01), (
         "The memory size of the "
         "Firecracker process "
         "changed from {} to {}.".format(before_size, after_size)