fix(bazel): integration test env variable expansion not respecting cu…

…stom variables

The integration test rule currently does not respect custom variables
that have been configured as part of the target. e.g. the following does
not work:

```bzl
integration_test(
  environment = {
    "TEST_ENV": "$(location blabla)"
  },
  commands = [
    "yarn test $${TEST_ENV}
  ],
)
```

This commit fixes that such custom variables are available for
expansion when commands are executed.

bazel/integration/test_runner/process_utils.ts

@@ -22,13 +22,16 @@ const environmentVariableSubstitutionRegex = /\${(\w+)}/g;
  *
  * @throws An error if a substituted environment variable does not exist.
  */
-export function expandEnvironmentVariableSubstitutions(args: string[]): string[] {
+export function expandEnvironmentVariableSubstitutions(
+  args: string[],
+  env: NodeJS.ProcessEnv,
+): string[] {
   return args.map((content) => {
     return content.replace(environmentVariableSubstitutionRegex, (_, variableName) => {
-      if (process.env[variableName] === undefined) {
+      if (env[variableName] === undefined) {
         throw new Error(`Could not find substituted environment variable: ${variableName}`);
       }
-      return process.env[variableName]!;
+      return env[variableName]!;
     });
   });
 }

bazel/integration/test_runner/runner.ts

@@ -218,7 +218,10 @@ export class TestRunner {
       const resolvedBinary = binary.containsExpandedValue
         ? await resolveBinaryWithRunfiles(binary.value)
         : binary.value;
-      const evaluatedArgs = expandEnvironmentVariableSubstitutions(args.map((v) => v.value));
+      const evaluatedArgs = expandEnvironmentVariableSubstitutions(
+        args.map((v) => v.value),
+        commandEnv,
+      );
       const success = await runCommandInChildProcess(
         resolvedBinary,
         evaluatedArgs,