sww tests: wait for the starting line as long as the start takes (closes #324)

A start on a loaded host can take longer than the 10-second wait for
a line. The new output.lineBeforeExit waits until the line is written
or sww exits, so only the test binary's own timeout ends the wait. It
replaces the waits that span the start in runUntilStopped,
TestServesUntilToldToStop and TestLogLevelHoldsBackTheLessSevereProcessLines.

Model: opus-5-5

internal/sww/sww_test.go

@@ -92,6 +92,31 @@ func (o *output) line(t *testing.T, key, value string) map[string]any {
 	return nil
 }
 
+// lineBeforeExit returns the first line whose msg is msg, waiting for it
+// while sww runs. It waits as long as that takes, so that a slow start
+// cannot fail the test, and fails the test if sww exits first.
+func (o *output) lineBeforeExit(
+	t *testing.T, msg string, exited <-chan int,
+) map[string]any {
+	t.Helper()
+
+	for {
+		fields := o.findLine(t, func(fields map[string]any) bool {
+			return fields["msg"] == msg
+		})
+		if fields != nil {
+			return fields
+		}
+
+		select {
+		case status := <-exited:
+			t.Fatalf("exit status %d while waiting for a line with msg %q; output:\n%s",
+				status, msg, o.text())
+		case <-time.After(pollInterval):
+		}
+	}
+}
+
 // findLine returns the first line written so far for which matches is true, or
 // nil.
 func (o *output) findLine(
@@ -236,11 +261,12 @@ func TestServesUntilToldToStop(t *testing.T) {
 	}()
 
 	// The default rule file is read.
-	if rules := out.line(t, "msg", "read the rule files")["rules"]; rules != 12.0 {
+	readRules := out.lineBeforeExit(t, "read the rule files", exited)
+	if rules := readRules["rules"]; rules != 12.0 {
 		t.Errorf("read %v rules from the default rule file, want 12", rules)
 	}
 
-	starting := out.line(t, "msg", "starting")
+	starting := out.lineBeforeExit(t, "starting", exited)
 	wantStartingLine(t, starting, dir)
 
 	addr, _ := starting["address"].(string)
@@ -286,7 +312,7 @@ func TestLogLevelHoldsBackTheLessSevereProcessLines(t *testing.T) {
 		}, out)
 	}()
 
-	out.line(t, "msg", "fetching a list failed")
+	out.lineBeforeExit(t, "fetching a list failed", exited)
 	stop()
 
 	select {
@@ -1261,7 +1287,7 @@ func runUntilStopped(
 		exited <- run(ctx, env, out)
 	}()
 
-	addr, _ := out.line(t, "msg", "starting")["address"].(string)
+	addr, _ := out.lineBeforeExit(t, "starting", exited)["address"].(string)
 	use("http://" + addr + "/")
 	stop()