add read_files tests

Author: GabrielSalla

tests/monitor_utils/sample_file.txt

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+Test file content

tests/monitor_utils/test_read_file.py

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+import pytest
+
+from monitor_utils import read_file
+
+
+def test_read_file():
+    """'read_file' should open a file relative to the file where the function was called"""
+    content = read_file("sample_file.txt")
+    assert content == "Test file content\n"
+
+
+@pytest.mark.parametrize("mode", ["a", "w", "wb"])
+def test_read_file_invalid_mode(mode):
+    """'read_file' should raise a ValueError if an invalid mode is passed"""
+    with pytest.raises(ValueError):
+        read_file("sample_file.txt", mode=mode)