Flush outputWriter's buffer when test finishes

suntala · suntala · commit 0eb55d72d25f · 2025-04-18T21:36:08.000+02:00
diff --git a/src/testing/sub_test.go b/src/testing/sub_test.go
@@ -1018,14 +1018,46 @@ func TestOutputWriter(t *T) {
 		buf: "cd",
 	}}
 	for _, tc := range testCases {
+		o.Write([]byte(tc.in))
+		if string(o.c.output) != tc.out {
+			t.Errorf("output:\ngot:\n%s\nwant:\n%s", o.c.output, tc.out)
+		}
+		if string(o.b) != tc.buf {
+			t.Errorf("buffer:\ngot:\n%s\nwant:\n%s", o.b, tc.buf)
+		}
+	}
+}
+
+func TestOutputWriterFlushing(t *T) {
+	tstate := newTestState(1, allMatcher())
+	buf := &strings.Builder{}
+	root := &T{
+		common: common{
+			w: buf,
+		},
+		tstate: tstate,
+	}
+
+	f := func(t *T) {
 		t.Run("", func(t *T) {
-			o.Write([]byte(tc.in))
-			if string(o.c.output) != tc.out {
-				t.Errorf("output:\ngot:\n%s\nwant:\n%s", o.c.output, tc.out)
-			}
-			if string(o.b) != tc.buf {
-				t.Errorf("buffer:\ngot:\n%s\nwant:\n%s", o.b, tc.buf)
-			}
+			t.o.Write([]byte("a\n"))
+			t.o.Write([]byte("b"))
+			t.Fail()
 		})
 	}
+	root.Run("check flushing of outputWriter", f)
+
+	got := strings.TrimSpace(buf.String())
+	output := `
+--- FAIL: check flushing of outputWriter (0.00s)
+    --- FAIL: check flushing of outputWriter/#00 (0.00s)
+        a
+        b
+	`
+
+	want := strings.TrimSpace(output)
+	re := makeRegexp(want)
+	if ok, err := regexp.MatchString(re, got); !ok || err != nil {
+		t.Errorf("output:\ngot:\n%s\nwant:\n%s", got, want)
+	}
 }
diff --git a/src/testing/testing.go b/src/testing/testing.go
@@ -629,7 +629,7 @@ type common struct {
 	mu          sync.RWMutex         // guards this group of fields
 	output      []byte               // Output generated by test or benchmark.
 	w           io.Writer            // For flushToParent.
-	o           io.Writer            // Writes output.
+	o           *outputWriter        // Writes output.
 	ran         bool                 // Test or benchmark (or one of its subtests) was executed.
 	failed      bool                 // Test or benchmark has failed.
 	skipped     bool                 // Test or benchmark has been skipped.
@@ -1118,6 +1118,14 @@ func (o *outputWriter) writeLine(b []byte) {
 	}
 }
 
+// flush outputs the contents of the buffer.
+func (o *outputWriter) flush() {
+	if len(o.b) == 0 {
+		return
+	}
+	o.Write([]byte("\n"))
+}
+
 // Log formats its arguments using default formatting, analogous to Println,
 // and records the text in the error log. For tests, the text will be printed only if
 // the test fails or the -test.v flag is set. For benchmarks, the text is always
@@ -1772,6 +1780,10 @@ func tRunner(t *T, fn func(t *T)) {
 				root.duration += highPrecisionTimeSince(root.start)
 				d := root.duration
 				root.mu.Unlock()
+				// Output the outputWriter's buffer.
+				if t.o != nil {
+					t.o.flush()
+				}
 				root.flushToParent(root.name, "--- FAIL: %s (%s)\n", root.name, fmtDuration(d))
 				if r := root.parent.runCleanup(recoverAndReturnPanic); r != nil {
 					fmt.Fprintf(root.parent.w, "cleanup panicked with %v", r)
@@ -1819,6 +1831,10 @@ func tRunner(t *T, fn func(t *T)) {
 			// test. See comment in Run method.
 			t.tstate.release()
 		}
+		// Output the outputWriter's buffer.
+		if t.o != nil {
+			t.o.flush()
+		}
 		t.report() // Report after all subtests have finished.
 
 		// Do not lock t.done to allow race detector to detect race in case
