fixing empty preamble trimming and add a test

Author: ialarmedalien

json_to_models/cli.py

@@ -240,7 +240,9 @@ def set_args(
 
         self.dict_keys_regex = [re.compile(rf"^{r}$") for r in dict_keys_regex] if dict_keys_regex else ()
         self.dict_keys_fields = dict_keys_fields or ()
-        self.preamble = preamble.strip() or None
+        if preamble:
+            preamble = preamble.strip()
+        self.preamble = preamble or None
         self.initialized = True
 
     @classmethod

test/test_cli/test_script.py

@@ -168,19 +168,53 @@ def test_script_custom(command):
 
 @pytest.mark.parametrize("command", test_commands)
 def test_add_preamble(command):
+
     PREAMBLE_TEXT = """
 # this is some test code
 # to be added to the file
 
 
 # let's see if it works
-    """
 
-    command += ' --preamble "' + PREAMBLE_TEXT + '"'
-    stdout = execute_test(command)
+
+    """
+    stdout = execute_test(command + ' --preamble "' + PREAMBLE_TEXT + '"')
     assert "let's see if it works" in stdout
 
 
+@pytest.mark.parametrize("command", test_commands)
+def test_add_trim_preamble(command):
+
+    def trim_header(line_string):
+        """remove the quoted command and everything from the first class declaration onwards"""
+        lines = line_string.splitlines()
+        start = 0
+        end = 0
+        line_no = 0
+        for l in lines:
+            if l.startswith('"""'):
+                start = line_no
+            if l.startswith('class '):
+                end = line_no
+                break
+            line_no += 1
+
+        return lines[start:end]
+
+    expected_result = execute_test(command)
+
+    BLANK_SPACE = """
+
+
+
+
+        """
+    # ensure blank space does not get propagated
+    stdout = execute_test(command + ' --preamble "' + BLANK_SPACE + '"')
+
+    assert trim_header(expected_result) == trim_header(stdout)
+
+
 wrong_arguments_commands = [
     pytest.param(f"""{executable} -l Model items "{test_data_path / 'photos.json'}" \
                                   -l Model - "{test_data_path / 'users.json'}" """, id="duplicate_name"),