tests/run-tests.py: Add general newline normalization function.

Add a general normalize_newlines() function that handles newline variations
(\\r\\r\\n, \\r\\n) to \\n while preserving literal \\r characters that are
part of test content.

This provides a robust solution for cross-platform test compatibility,
particularly addressing PTY double-newline issues that can occur with some
terminal implementations.

The function is applied to all test output before comparison, eliminating
platform-specific newline issues.

Includes a unit test to verify the normalization behavior.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

.gitattributes

@@ -18,6 +18,7 @@
 # These should also not be modified by git.
 tests/basics/string_cr_conversion.py -text
 tests/basics/string_crlf_conversion.py -text
+tests/micropython/test_normalize_newlines.py.exp -text
 ports/stm32/pybcdc.inf_template -text
 ports/stm32/usbhost/** -text
 ports/cc3200/hal/aes.c -text

pyproject.toml

@@ -74,5 +74,6 @@ exclude = [
   "tests/basics/*.py",
   "tests/*/repl_*.py",
   "tests/cmdline/cmd_compile_only_error.py",
+  "tests/micropython/test_normalize_newlines.py",
   "tests/micropython/viper_args.py",
 ]

tests/micropython/test_normalize_newlines.py

@@ -0,0 +1,14 @@
+# Test for normalize_newlines functionality
+# This test verifies that test framework handles various newline combinations correctly
+
+# Note: This is more of an integration test since normalize_newlines is in the test framework
+# The actual testing happens when this test is run through run-tests.py
+
+print("Testing newline handling")
+print("Line 1\r\nLine 2")  # Windows-style line ending - should be normalized
+print("Line 3")            # Normal line
+print("Line 4")            # Normal line
+print("Line 5\nLine 6")    # Unix-style line ending - already normalized
+
+# Test that literal \r in strings is preserved
+print(repr("test\rstring"))  # Should show 'test\rstring' not 'test\nstring'

tests/micropython/test_normalize_newlines.py.exp

@@ -0,0 +1,8 @@
+Testing newline handling
+Line 1
+Line 2
+Line 3
+Line 4
+Line 5
+Line 6
+'test\rstring'

tests/run-tests.py

@@ -60,6 +60,23 @@ DIFF = os.getenv("MICROPY_DIFF", "diff -u")
 # Set PYTHONIOENCODING so that CPython will use utf-8 on systems which set another encoding in the locale
 os.environ["PYTHONIOENCODING"] = "utf-8"
 
+
+def normalize_newlines(data):
+    """Normalize newline variations to \\n.
+
+    Only normalizes actual line endings, not literal \\r characters in strings.
+    Handles \\r\\r\\n and \\r\\n cases to ensure consistent comparison
+    across different platforms and terminals.
+    """
+    if isinstance(data, bytes):
+        # Handle PTY double-newline issue first
+        data = data.replace(b"\r\r\n", b"\n")
+        # Then handle standard Windows line endings
+        data = data.replace(b"\r\n", b"\n")
+        # Don't convert standalone \r as it might be literal content
+    return data
+
+
 # Code to allow a target MicroPython to import an .mpy from RAM
 # Note: the module is named `__injected_test` but it needs to have `__name__` set to
 # `__main__` so that the test sees itself as the main module, eg so unittest works.
@@ -706,7 +723,7 @@ def run_micropython(pyb, args, test_file, test_file_abspath, is_special=False):
         )
 
     # canonical form for all ports/platforms is to use \n for end-of-line
-    output_mupy = output_mupy.replace(b"\r\n", b"\n")
+    output_mupy = normalize_newlines(output_mupy)
 
     # don't try to convert the output if we should skip this test
     if had_crash or output_mupy in (b"SKIP\n", b"SKIP-TOO-LARGE\n", b"CRASH"):