Automated source conversion transforms a program’s representation using a defined set of rules. It can change syntax, language, or supporting runtime conventions. The resulting source remains one part of an application whose behavior also depends on libraries, data representations, external interfaces, and deployment conditions.
A conversion result needs separate answers about transformation coverage, runtime capability, behavioral equivalence, and maintainability. A high percentage of processed source does not combine those questions into a demonstrated application outcome.
Syntax and runtime support differ
Babel provides a bounded JavaScript example: syntax transformation and polyfills for missing runtime features are separate mechanisms. Rewriting an expression does not itself supply every capability expected from the target environment.
The TypeScript Handbook illustrates another boundary. Type annotations are erased from emitted JavaScript; their presence in source does not add runtime validation of incoming values. Successful compilation therefore cannot be interpreted as evidence of checks the generated program does not perform.
These examples explain distinctions within their documented ecosystems. They provide no conversion-success rate for COBOL, VB6, or another source language. A candidate tool needs evidence for its actual dialects and constructs.
Coverage needs a behavior inventory
The input inventory should include language features, runtime services, libraries, external calls, encodings, numeric representations, and operational entry points. Counting files or lines alone cannot reveal whether an unsupported construct sits on a critical path.
A representative conversion should classify behavior as supported, manually repaired, or unresolved. Unsupported features need explicit disposition. Omitting them from the denominator can make a reported conversion percentage look complete while leaving required work unimplemented.
The sample should include difficult behavior deliberately: error paths, numeric boundaries, batch processing, and interactions with external components. A small, isolated calculation is insufficient evidence for an application whose essential work crosses those boundaries.
Generated dependencies are part of the result
A compatibility runtime can preserve conventions that the target language does not provide directly. That can be a useful implementation choice, but its version, licensing, support, deployment, and replacement implications belong in the assessment.
The emitted language name therefore does not describe the entire target architecture. Source expressed in a familiar language can still depend on proprietary services or require specialized knowledge of the conversion framework.
Clean deployment tests help expose these dependencies. A working result on the conversion machine can rely on installed components that were never captured in the deliverable.
Equivalence needs controlled comparison
Source and target executions need comparable starting state, inputs, and observation boundaries. Otherwise a difference can originate in the test conditions rather than the transformed implementation.
Required comparisons include business outputs, data changes, error behavior, and transaction outcomes. A known defect in the source should be classified separately from behavior that must remain equivalent. Preserving every observed result without that decision can preserve unwanted behavior.
AWS’s mainframe conversion examples assume particular source and target arrangements, while its shared-Db2 replatforming guidance separately describes transaction and data comparison. Those scoped examples support testing obligations, not an unconditional equivalence guarantee.
The next change tests the maintenance claim
The receiving team should reproduce the conversion build and perform a representative maintenance change. That exercise reveals whether changes belong in source, generated output, templates, or runtime extensions, and whether regeneration preserves them.
Acceptance needs demonstrated behavior, an understood dependency chain, and a workable change path. Conversion has completed a useful transformation when these properties hold for the agreed scope; source emission alone establishes a narrower technical milestone.