MLBEDSW-2067: added custom exceptions

Added custom exceptions to handle different types of input errors.

Also performed minor formatting changes using flake8/black.

Change-Id: Ie5b05361507d5e569aff045757aec0a4a755ae98
Signed-off-by: Louis Verhaard <louis.verhaard@arm.com>
diff --git a/ethosu/vela/test/test_model_reader.py b/ethosu/vela/test/test_model_reader.py
new file mode 100644
index 0000000..ee9a51e
--- /dev/null
+++ b/ethosu/vela/test/test_model_reader.py
@@ -0,0 +1,40 @@
+# Copyright (C) 2020 Arm Limited or its affiliates. All rights reserved.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the License); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an AS IS BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# Description:
+# Unit tests for model_reader.
+import pytest
+from ethosu.vela import model_reader
+from ethosu.vela.errors import InputFileError
+
+
+def test_read_model_incorrect_extension(tmpdir):
+    # Tests read_model with a file name that does not end with .tflite
+    with pytest.raises(InputFileError):
+        model_reader.read_model("no_tflite_file.txt", model_reader.ModelReaderOptions())
+
+
+def test_read_model_corrupt_contents(tmpdir):
+    # Tests read_model with a corrupt .tflite file
+    fname = tmpdir.join("corrupt.tflite")
+    fname.write("abcde1234")
+    with pytest.raises(InputFileError):
+        model_reader.read_model(fname.strpath, model_reader.ModelReaderOptions())
+
+
+def test_read_model_file_not_found(tmpdir):
+    # Tests read_model with a .tflite file that does not exist
+    with pytest.raises(InputFileError):
+        model_reader.read_model("non_existing.tflite", model_reader.ModelReaderOptions())