Add documentation to k6 exit codes definitions (#3200)

Co-authored-by: Oleg Bespalov <[email protected]>

errext/exitcodes/codes.go

@@ -8,17 +8,49 @@ type ExitCode uint8
 
 // list of exit codes used by k6
 const (
-	CloudTestRunFailed       ExitCode = 97 // This used to be 99 before k6 v0.33.0
+	// CloudTestRunFailed indicates that the cloud test run failed.
+	// Its value used to be 99 before k6 v0.33.0.
+	CloudTestRunFailed ExitCode = 97 // This used to be 99 before k6 v0.33.0
+
+	// CloudFailedToGetProgress indicates that k6 was unable to synchronize the
+	// test progress with the cloud.
 	CloudFailedToGetProgress ExitCode = 98
-	ThresholdsHaveFailed     ExitCode = 99
-	SetupTimeout             ExitCode = 100
-	TeardownTimeout          ExitCode = 101
-	GenericTimeout           ExitCode = 102 // TODO: remove?
+
+	// ThresholdsHaveFailed indicates that one or more thresholds have failed.
+	ThresholdsHaveFailed ExitCode = 99
+
+	// SetupTimeout indicates the execution of the test setup function timed out.
+	SetupTimeout ExitCode = 100
+
+	// TeardownTimeout indicates the execution of the test teardown function timed out.
+	TeardownTimeout ExitCode = 101
+
+	// GenericTimeout indicates a timeout with an unspecified reason.
+	GenericTimeout ExitCode = 102 // TODO: remove?
+
+	// ScriptStoppedFromRESTAPI indicates the execution has been
+	// stopped by a call to the k6's REST API.
 	ScriptStoppedFromRESTAPI ExitCode = 103
-	InvalidConfig            ExitCode = 104
-	ExternalAbort            ExitCode = 105
-	CannotStartRESTAPI       ExitCode = 106
-	ScriptException          ExitCode = 107
-	ScriptAborted            ExitCode = 108
-	GoPanic                  ExitCode = 109
+
+	// InvalidConfig indicates an invalid configuration.
+	InvalidConfig ExitCode = 104
+
+	// ExternalAbort indicates the test was aborted by an external signal
+	// (e.g. SIGINT, SIGTERM, etc.) and should be considered aborted rather
+	// than a failure.
+	ExternalAbort ExitCode = 105
+
+	// CannotStartRESTAPI indicates the k6's REST API server could not be started.
+	CannotStartRESTAPI ExitCode = 106
+
+	// ScriptException indicates an exception was thrown during the
+	// test script's execution.
+	ScriptException ExitCode = 107
+
+	// ScriptAborted indicates the script was aborted by a call to the
+	// k6 execution module's `test.abort()` function.
+	ScriptAborted ExitCode = 108
+
+	// GoPanic indicates the script was aborted by a panic in the Go runtime.
+	GoPanic ExitCode = 109
 )