Fix swift-testing test not always capturing terminal output (#1129)

Occasionally a swift-testing test can start printing output before the
test start JSON event is recieved over the named pipe. This output was
always recorded to the test run, but wasn't necessarily captured in the
structure used to record test results for the vscode-swift unit tests.

This would cause the `swift-testing: Runs passing test` test to
occasionally fail when it couldn't find the output line printed during
the test, because it was printed before the test start event was
recieved.

Record the output no matter when it occurs so that it can be verified in
the tests correctly.

Author: plemarquand

src/TestExplorer/TestRunner.ts

@@ -148,7 +148,7 @@ export class TestRunProxy {
 
         // Forward any output captured before the testRun was created.
         for (const outputLine of this.queuedOutput) {
-            this.testRun.appendOutput(outputLine);
+            this.performAppendOutput(this.testRun, outputLine);
         }
         this.queuedOutput = [];
 
@@ -227,17 +227,29 @@ export class TestRunProxy {
     public appendOutput(output: string) {
         const tranformedOutput = this.prependIterationToOutput(output);
         if (this.testRun) {
-            this.testRun.appendOutput(tranformedOutput);
-            this.runState.output.push(tranformedOutput);
+            this.performAppendOutput(this.testRun, tranformedOutput);
         } else {
             this.queuedOutput.push(tranformedOutput);
         }
     }
 
     public appendOutputToTest(output: string, test: vscode.TestItem, location?: vscode.Location) {
         const tranformedOutput = this.prependIterationToOutput(output);
-        this.testRun?.appendOutput(tranformedOutput, location, test);
-        this.runState.output.push(tranformedOutput);
+        if (this.testRun) {
+            this.performAppendOutput(this.testRun, tranformedOutput, location, test);
+        } else {
+            this.queuedOutput.push(tranformedOutput);
+        }
+    }
+
+    private performAppendOutput(
+        testRun: vscode.TestRun,
+        output: string,
+        location?: vscode.Location,
+        test?: vscode.TestItem
+    ) {
+        testRun.appendOutput(output, location, test);
+        this.runState.output.push(output);
     }
 
     private prependIterationToOutput(output: string): string {