Tests

Treat NotImplemented as a singleton type #20165

Job	Run time
Test mypyc suite with 32-bit Python	3m 5s
Type check our own code (py310-ubuntu)	1m 39s
Test suite with py314-windows-64	2m 58s
Test suite with py312-ubuntu	3m 3s
Test suite with py311-ubuntu	3m 3s
Test suite with py314t-ubuntu, mypyc-compiled	3m 2s
Type check our own code (py310-windows-64)	2m 15s
Formatting and code style with Black + ruff	1m 58s
Test suite with py313-ubuntu, mypyc-compiled	3m 2s
Parallel tests with py314-ubuntu, mypyc-compiled	3m 2s
Test suite with py314-ubuntu, mypyc-compiled	3m 1s
mypyc runtime tests with py310-ubuntu	3m 5s
Test suite with py310-ubuntu, mypyc-compiled	3m 2s
mypyc runtime tests with py313-macos	3m 7s
Parallel tests with py314-ubuntu, interpreted	3m 3s
	42m 25s

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