Add Test-Toml function for validation

[MariusStorhaug]

Scripts that load TOML content from external sources need to validate it before parsing. Once ConvertFrom-Toml lands (#2), the only signal of invalid input will be a thrown exception. PowerShell's Test-Json sets the established pattern for serialization-format validators: returns [bool], writes parser errors to the error stream when invalid.

Request

Desired capability

Test-Toml -Path Cargo.toml          # validate a file
$content | Test-Toml                 # validate a string
'[invalid' | Test-Toml               # returns $false, writes error

Parameters

Parameter	Description
-Path	File path to validate (parameter set: Path)
-LiteralPath	Literal path (parameter set: LiteralPath)
-InputObject	String to validate (ValueFromPipeline, default set)

Acceptance criteria

• Returns $true when content is valid TOML 1.0 (or 1.1, depending on parser scope from Add ConvertFrom-Toml and ConvertTo-Toml functions with full TOML v1.1.0 spec coverage #2)
• Returns $false when content is invalid; the parser error is written to the error stream
• Accepts pipeline input as a string
• Mirrors Test-Json parameter shape and behavior

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Technical decisions

Implementation: Wraps ConvertFrom-Toml in try/catch. On exception, writes the parser error via Write-Error and returns $false. On success, returns $true.

Function placement: src/functions/public/Test-Toml.ps1.

No new parser logic: Reuses the existing ConvertFrom-Toml parser. This keeps validation behavior consistent with parsing behavior.

Output type: [bool] only — never throws on invalid input.

Alias: Test-Tml, matching the planned alias pattern in #2.

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Implementation plan

• Add Test-Toml in src/functions/public/Test-Toml.ps1 with Test-Tml alias
• Add Pester tests — valid string, invalid string, valid file, invalid file, pipeline input, error-stream contents on failure
• Update README with usage example

Related

• Add ConvertFrom-Toml and ConvertTo-Toml functions with full TOML v1.1.0 spec coverage #2 — ConvertFrom-Toml (prerequisite)