[T-004] Add comprehensive test suite for flux-py VM

[SuperInstance]

Summary

• Added pytest test framework (previously 0 tests)
• Created test suite covering VM execution, assembler, disassembler, vocabulary, and interpreter
• 84 tests across 3 test files, all passing in 0.22s

Test Coverage

VM Core (24 tests)

• Basic execution: MOVI + HALT, multiple registers, empty bytecode, max cycles
• Arithmetic: IADD (positive, negative), IMUL (normal, zero), IDIV (normal, truncation, div-by-zero), DEC (normal, negative)
• Control flow: JNZ taken/not-taken, loop with DEC+JNZ, factorial loop, sum 1..10
• Error handling: unknown opcode, truncated bytecode (MOVI, IADD), error returns None
• Register access: all 16 default zero, out-of-bounds returns 0, specific register result
• Opcodes constant verification

Assembler & Disassembler (32 tests)

• All 7 opcodes encoded correctly (HALT, MOVI, IADD, IMUL, IDIV, DEC, JNZ)
• Label resolution: forward jumps, backward jumps, labels on own line, unresolved label error
• Comments: # and ; styles, comments between instructions
• Error cases: unknown mnemonic
• Multi-instruction programs: (3+4)*2=14, factorial(5)=120
• Round-trips: assemble→execute, assemble→disassemble
• Disassembler: all opcodes, unknown opcode, address prefixes, empty bytecode

Vocabulary & Interpreter (28 tests)

• Pattern matching: add/match, return fields (assembly, result_reg, description), no-match, empty vocab
• Case-insensitive matching, first-match-wins
• Built-in vocabulary: 5 patterns, group extraction for all patterns
• Interpreter: all 5 built-in commands (add, mul, factorial, double, square)
• Edge cases: factorial(1), no-match, custom vocabulary, cycle count in message

Testing

python -m pytest tests/ -v → 84 passed in 0.22s

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[beta-devin-ai-integration]

Devin Review found 1 potential issue.

View 4 additional findings in Devin Review.

[beta-devin-ai-integration]

🟡 test_max_cycles_limit doesn't actually test the max_cycles limit

The test claims to verify "VM should stop after max_cycles even if not halted" but the bytecode movi(0, 1) is a single 4-byte instruction. After executing it, PC=4 equals len(bc)=4, so the VM loop exits due to the self.pc < len(self.bc) condition at flux_vm.py:64 — NOT because max_cycles=5 was reached. The self.cycles < self.max_cycles condition is never the limiting factor. If someone removed the max_cycles check from the VM's while loop, this test would still pass, providing a false sense of regression protection for that feature. The test needs bytecode containing a loop (e.g., using JNZ to jump backward) so that the max_cycles limit is actually what terminates execution.

Suggested change

	def test_max_cycles_limit(self):
	"""VM should stop after max_cycles even if not halted."""
	# MOVI R0, 1 — no HALT, so it would loop forever
	bc = movi(0, 1)
	vm = FluxVM(bc, max_cycles=5).execute()
	assert not vm.halted
	assert vm.cycles == 1 # only 1 instruction in bytecode
	def test_max_cycles_limit(self):
	"""VM should stop after max_cycles even if not halted."""
	# Infinite loop: MOVI R0, 1; JNZ R0, -4 (jumps back to JNZ itself)
	bc = movi(0, 1) + jnz(0, -4)
	vm = FluxVM(bc, max_cycles=5).execute()
	assert not vm.halted
	assert vm.cycles == 5

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