tests/extmod/vfs_blockdev_invalid.py: Handle low memory conditions.

This commit modifies the "extmod/vfs_blockdev_invalid" test to better
behave on boards with low available memory.

Before these changes the test would fail on ESP8266 (at least), due to
low memory, but in a way that could not be easily solved as the error
occurred in the middle of the test.

The test has been rewritten to delay its output until the very end, so
if a low memory condition occurs and needs to stop execution then no
real output will show up before the skip marker.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

tests/extmod/vfs_blockdev_invalid.py

@@ -46,12 +46,16 @@ class RAMBlockDevice:
 try:
     bdev = RAMBlockDevice(50)
 except MemoryError:
-    print("SKIP")
+    print("SKIP-TOO-LARGE")
     raise SystemExit
 
 
-def test(vfs_class):
-    print(vfs_class)
+ERROR_EIO = (OSError, "[Errno 5] EIO")
+ERROR_EINVAL = (OSError, "[Errno 22] EINVAL")
+ERROR_TYPE = (TypeError, "can't convert str to int")
+
+
+def test(vfs_class, test_data):
     bdev.read_res = 0  # reset function results
     bdev.write_res = 0
 
@@ -61,17 +65,15 @@ def test(vfs_class):
     with fs.open("test", "w") as f:
         f.write("a" * 64)
 
-    for res in (0, -5, 5, 33, "invalid"):
-        # -5 is a legitimate negative failure (EIO), positive integer
-        # is not
-
+    for res, error_open, error_read in test_data:
         # This variant will fail on open
         bdev.read_res = res
         try:
             with fs.open("test", "r") as f:
-                print("opened")
+                assert error_open is None
         except Exception as e:
-            print(type(e), e)
+            assert error_open is not None
+            assert (type(e), str(e)) == error_open
 
         # This variant should succeed on open, may fail on read
         # unless the filesystem cached the contents already
@@ -79,11 +81,35 @@ def test(vfs_class):
         try:
             with fs.open("test", "r") as f:
                 bdev.read_res = res
-                print("read 1", f.read(1))
-                print("read rest", f.read())
+                assert f.read(1) == "a"
+                assert f.read() == "a" * 63
+                assert error_read is None
         except Exception as e:
-            print(type(e), e)
+            assert error_read is not None
+            assert (type(e), str(e)) == error_read
 
 
-test(vfs.VfsLfs2)
-test(vfs.VfsFat)
+try:
+    test(
+        vfs.VfsLfs2,
+        (
+            (0, None, None),
+            (-5, ERROR_EIO, None),
+            (5, ERROR_EINVAL, None),
+            (33, ERROR_EINVAL, None),
+            ("invalid", ERROR_TYPE, None),
+        ),
+    )
+    test(
+        vfs.VfsFat,
+        (
+            (0, None, None),
+            (-5, ERROR_EIO, ERROR_EIO),
+            (5, ERROR_EIO, ERROR_EIO),
+            (33, ERROR_EIO, ERROR_EIO),
+            ("invalid", ERROR_TYPE, ERROR_TYPE),
+        ),
+    )
+    print("OK")
+except MemoryError:
+    print("SKIP-TOO-LARGE")

tests/extmod/vfs_blockdev_invalid.py.exp

@@ -1,28 +1 @@
-<class 'VfsLfs2'>
-opened
-read 1 a
-read rest aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-<class 'OSError'> [Errno 5] EIO
-read 1 a
-read rest aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-<class 'OSError'> [Errno 22] EINVAL
-read 1 a
-read rest aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-<class 'OSError'> [Errno 22] EINVAL
-read 1 a
-read rest aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-<class 'TypeError'> can't convert str to int
-read 1 a
-read rest aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-<class 'VfsFat'>
-opened
-read 1 a
-read rest aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-<class 'OSError'> [Errno 5] EIO
-<class 'OSError'> [Errno 5] EIO
-<class 'OSError'> [Errno 5] EIO
-<class 'OSError'> [Errno 5] EIO
-<class 'OSError'> [Errno 5] EIO
-<class 'OSError'> [Errno 5] EIO
-<class 'TypeError'> can't convert str to int
-<class 'TypeError'> can't convert str to int
+OK