PULUMI_CONFIG env variable is not used with PulumiTest

What happened?

Trying to use a configuration JSON during testing via the environment variable at runtime - as is the case with the implementation in other languages.

Example

Given '{"project:the_environment": "devtest"}' stored in PULUMI_CONFIG

final var config = ctx.config();
final var environment = config.get("the_environment")

fails when testing via PulumiTest

Output of pulumi about

CLI
Version      3.108.1
Go Version   go1.22.0
Go Compiler  gc

Plugins
NAME        VERSION
aws         6.18.2
aws-native  0.95.0
java        unknown

Host
OS       darwin
Version  14.4
Arch     x86_64

Additional context

Instead of initialising an empty config in PulumiTestInternal

if (this.config == null) {
                this.config = new DeploymentImpl.Config(ImmutableMap.of(), ImmutableSet.of());
}

it should be possible and safe to do

if (this.config == null) {
                this.config = Config.parse();
}

instead.

Contributing

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To contribute a fix for this issue, leave a comment (and link to your pull request, if you've opened one already).

Start by reading PulumiTestInternal and Config.parse, focusing on how the default configuration is initialized when PulumiTest runs. Use the Java example with PULUMI_CONFIG as the regression case, and confirm that ctx.config().get("the_environment") reads the supplied value instead of an empty configuration.