DSC Resource manifest test property schema reference

Article
05/10/2024

Synopsis

Defines how to test whether a DSC Resource instance is in the desired state.

Metadata

SchemaDialect: https://json-schema.org/draft/2020-12/schema
SchemaID:      https://raw.githubusercontent.com/PowerShell/DSC/main/schemas/2024/04/resource/manifest.test.json
Type:          object

Description

If a DSC Resource implements its own logic for determining whether an instance is in the desired state, it must define the test property in its manifest. This property defines how DSC can call the resource to test whether an instance is in the desired state.

When this property isn't defined, DSC uses a synthetic test method for the resource. The synthetic test method:

Gets the actual state of the instance using the resource's get method.
Compares every defined property of the instance's desired state to the actual state.
If the desired state of a property isn't equal to the actual state of that property, DSC reports that the instance isn't in the desired state.

Because the synthetic test only checks for equivalency, it can't accurately test resources with properties that can't be evaluated with equivalency alone. For example, if a resource manages package versions and allows setting the version to latest, DSC would report an instance with a version of 3.1.0 as being out of the desired state, even if 3.1.0 is the latest version of the package.

For resources with properties that can't be evaluated by equivalency alone, always define the test property in the manifest.

DSC sends data to the command in three ways:

When input is stdin, DSC sends the data as a string representing the data as a compressed JSON object without spaces or newlines between the object properties.
When input is env, DSC sends the data as environment variables. It creates an environment variable for each property in the input data object, using the name and value of the property.
When the args array includes a JSON input argument definition, DSC sends the data as a string representing the data as a compressed JSON object to the specified argument.

If you don't define the input property and don't define a JSON input argument, DSC can't pass the input JSON to the resource. You can only define one JSON input argument for a command.

You must define the input property, one JSON input argument in the args property array, or both.

Examples

Example 1 - Full definition

This example is from the Microsoft.Windows/Registry DSC Resource.

"test": {
  "executable": "registry",
  "args": [
    "config",
    "test"
  ],
  "input": "stdin",
  "return": "state"
}

It defines executable as registry, rather than registry.exe. The extension isn't required when the operating system recognizes the command as an executable.

The manifest defines two arguments, config and test. The value of the input property indicates that the test command expects its input as a JSON blob from stdin.

Combined with the value for executable, DSC calls the test method for this resource by running:

{ ... } | registry config test

The manifest defines return as state, indicating that it only returns the actual state of the resource when the test method runs.

Required Properties

The test definition must include these properties:

executable

Properties

executable

The executable property defines the name of the command to run. The value must be the name of a command discoverable in the system's PATH environment variable or the full path to the command. A file extension is only required when the command isn't recognizable by the operating system as an executable.

Type:     string
Required: true

args

The args property defines the list of arguments to pass to the command. The arguments can be any number of strings. If you want to pass the JSON object representing the property bag for the resource to an argument, you can define a single item in the array as a [JSON object], indicating the name of the argument with the jsonInputArg string property and whether the argument is mandatory for the command with the mandatory boolean property.

Type:     array
Required: false
Default:  []
Type:     [string, object(JSON Input Argument)]

String arguments

Any item in the argument array can be a string representing a static argument to pass to the command, like config or --format.

Type: string

JSON input argument

Defines an argument for the command that accepts the JSON input object as a string. DSC passes the JSON input to the named argument when available. A JSON input argument is defined as a JSON object with the following properties:

jsonInputArg (required) - the argument to pass the JSON data to for the command, like --input.
mandatory (optional) - Indicate whether DSC should always pass the argument to the command, even when there's no JSON input for the command. In that case, DSC passes an empty string to the JSON input argument.

You can only define one JSON input argument per arguments array.

If you define a JSON input argument and an input kind for a command, DSC sends the JSON data both ways:

If you define input as env and a JSON input argument, DSC sets an environment variable for each property in the JSON input and passes the JSON input object as a string to the defined argument.
If you define input as stdin and a JSON input argument, DSC passes the JSON input over stdin and as a string to the defined argument.
If you define a JSON input argument without defining the input property, DSC only passes the JSON input as a string to the defined argument.

If you don't define the input property and don't define a JSON input argument, DSC can't pass the input JSON to the resource. This makes the manifest invalid. You must define the input property, a JSON input argument in the args property array, or both.

Type:                object
RequiredProperties: [jsonInputArg]

input

The input property defines how to pass input to the resource. If this property isn't defined, DSC doesn't send any input to the resource when invoking the test operation.

The value of this property must be one of the following strings:

env - Indicates that the resource expects the properties of an instance to be specified as environment variables with the same names and casing.

This option only supports the following data types for instance properties:
- boolean
- integer
- number
- string
- array of integer values
- array of number values
- array of string values
For non-array values, DSC sets the environment variable to the specified value as-is. When the data type is an array of values, DSC sets the environment variable as a comma-delimited string. For example, the property foo with a value of [1, 2, 3] is saved in the foo environment variable as "1,2,3".

If the resource needs to support complex properties with an object value or multi-type arrays, set this to stdin instead.
stdin - Indicates that the resource expects a JSON blob representing an instance from stdin. The JSON must adhere to the instance schema for the resource.

Type:        string
Required:    false
ValidValues: [env, stdin]

return

The return property defines how DSC should process the output for this method. The value of this property must be one of the following strings:

state - Indicates that the resource returns only the instance's actual state.
stateAndDiff - Indicates that the resource returns the instance's actual state and an array of property names that are out of the desired state.

The default value is state.

Type:        string
Required:    false
Default:     state
ValidValues: [state, stateAndDiff]

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