Fix bug where test_output writes to ./- instead of stdout

Also remove gibberish from test_output

ovgenpy/outputs.py

@@ -3,7 +3,7 @@ import shlex
 import subprocess
 from abc import ABC, abstractmethod
 from os.path import abspath
-from typing import TYPE_CHECKING, Type, List, Union
+from typing import TYPE_CHECKING, Type, List, Union, Optional
 
 from ovgenpy.config import register_config
 
@@ -124,7 +124,8 @@ class PipeOutput(Output):
 
 @register_config
 class FFmpegOutputConfig(IOutputConfig):
-    path: str
+    # path=None writes to stdout.
+    path: Optional[str]
     args: str = ''
 
     # Do not use `-movflags faststart`, I get corrupted mp4 files (missing MOOV)
@@ -142,7 +143,13 @@ class FFmpegOutput(PipeOutput):
         ffmpeg = _FFmpegCommand([FFMPEG, '-y'], ovgen_cfg)
         ffmpeg.add_output(cfg)
         ffmpeg.templates.append(cfg.args)
-        self.open(ffmpeg.popen([abspath(cfg.path)], self.bufsize))
+
+        if cfg.path is None:
+            video_path = '-'    # Write to stdout
+        else:
+            video_path = abspath(cfg.path)
+
+        self.open(ffmpeg.popen([video_path], self.bufsize))
 
 
 # FFplayOutput

tests/test_output.py

@@ -1,3 +1,4 @@
+from pathlib import Path
 from typing import TYPE_CHECKING
 
 import pytest
@@ -13,14 +14,13 @@ if TYPE_CHECKING:
     import pytest_mock
 
 CFG = default_config(render=RendererConfig(WIDTH, HEIGHT))
-STDOUT_CFG = FFmpegOutputConfig('-', '-f nut')
+NULL_CFG = FFmpegOutputConfig(None, '-f null')
 
 
 def test_render_output():
     """ Ensure rendering to output does not raise exceptions. """
     renderer = MatplotlibRenderer(CFG.render, CFG.layout, nplots=1)
-    output_cfg = FFmpegOutputConfig('-', '-f nut')
-    out = FFmpegOutput(CFG, output_cfg)
+    out: FFmpegOutput = NULL_CFG(CFG)
 
     renderer.render_frame([ALL_ZEROS])
     out.write_frame(renderer.get_frame())
@@ -29,12 +29,14 @@ def test_render_output():
 
 
 def test_output():
-    out = FFmpegOutput(CFG, STDOUT_CFG)
+    out: FFmpegOutput = NULL_CFG(CFG)
 
     frame = bytes(WIDTH * HEIGHT * RGB_DEPTH)
     out.write_frame(frame)
 
     assert out.close() == 0
+    # Ensure video is written to stdout, and not current directory.
+    assert not Path('-').exists()
 
 
 # Ensure ovgen terminates FFplay upon exceptions.