testing: make indentation consistent in sub-tests

Instead of mixed usage of spaces and tabs for indentation,
just use 4 spaces instead of one tab.

This test:

func TestX(t *testing.T) {
	t.Error("1\nnew line")
	t.Error("2")
	t.Error("3")
	t.Run("Y", func(t *testing.T) {
		t.Error("2")
		t.Error("2b\nnew line")
		t.Run("Z", func(t *testing.T) {
			t.Error("3\nnew line")
		})
	})
	t.Error("4")
}

produces following output:

--- FAIL: TestX (0.00s)
    indent_test.go:6: 1
	new line
    indent_test.go:7: 2
    indent_test.go:8: 3
    --- FAIL: TestX/Y (0.00s)
	indent_test.go:10: 2
	indent_test.go:11: 2b
	    new line
	--- FAIL: TestX/Y/Z (0.00s)
	    indent_test.go:13: 3
		new line
    indent_test.go:16: 4
FAIL

Fixes #25369

Change-Id: Ib3b5da45ab3ee670c6e8a23172e7cbefb94c5e60
Reviewed-on: https://go-review.googlesource.com/113177
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

src/cmd/go/go_test.go

@@ -4892,30 +4892,30 @@ func TestTestRegexps(t *testing.T) {
 	//	BenchmarkX/Y is run in full, twice
 	want := `=== RUN   TestX
 === RUN   TestX/Y
-	x_test.go:6: LOG: X running
-    	x_test.go:8: LOG: Y running
+    x_test.go:6: LOG: X running
+        x_test.go:8: LOG: Y running
 === RUN   TestXX
-	z_test.go:10: LOG: XX running
+    z_test.go:10: LOG: XX running
 === RUN   TestX
 === RUN   TestX/Y
-	x_test.go:6: LOG: X running
-    	x_test.go:8: LOG: Y running
+    x_test.go:6: LOG: X running
+        x_test.go:8: LOG: Y running
 === RUN   TestXX
-	z_test.go:10: LOG: XX running
+    z_test.go:10: LOG: XX running
 --- BENCH: BenchmarkX/Y
-	x_test.go:15: LOG: Y running N=1
-	x_test.go:15: LOG: Y running N=100
-	x_test.go:15: LOG: Y running N=10000
-	x_test.go:15: LOG: Y running N=1000000
-	x_test.go:15: LOG: Y running N=100000000
-	x_test.go:15: LOG: Y running N=2000000000
+    x_test.go:15: LOG: Y running N=1
+    x_test.go:15: LOG: Y running N=100
+    x_test.go:15: LOG: Y running N=10000
+    x_test.go:15: LOG: Y running N=1000000
+    x_test.go:15: LOG: Y running N=100000000
+    x_test.go:15: LOG: Y running N=2000000000
 --- BENCH: BenchmarkX/Y
-	x_test.go:15: LOG: Y running N=1
-	x_test.go:15: LOG: Y running N=2000000000
+    x_test.go:15: LOG: Y running N=1
+    x_test.go:15: LOG: Y running N=2000000000
 --- BENCH: BenchmarkX
-	x_test.go:13: LOG: X running N=1
+    x_test.go:13: LOG: X running N=1
 --- BENCH: BenchmarkXX
-	z_test.go:18: LOG: XX running N=1
+    z_test.go:18: LOG: XX running N=1
 `
 
 	have := strings.Join(lines, "")

src/testing/sub_test.go

@@ -168,7 +168,7 @@ func TestTRun(t *T) {
 --- FAIL: failure in parallel test propagates upwards (N.NNs)
     --- FAIL: failure in parallel test propagates upwards/#00 (N.NNs)
         --- FAIL: failure in parallel test propagates upwards/#00/par (N.NNs)
-		`,
+        `,
 		f: func(t *T) {
 			t.Run("", func(t *T) {
 				t.Parallel()
@@ -210,8 +210,8 @@ func TestTRun(t *T) {
 		desc: "skipping after error",
 		output: `
 --- FAIL: skipping after error (N.NNs)
-	sub_test.go:NNN: an error
-	sub_test.go:NNN: skipped`,
+    sub_test.go:NNN: an error
+    sub_test.go:NNN: skipped`,
 		f: func(t *T) {
 			t.Error("an error")
 			t.Skip("skipped")
@@ -320,9 +320,9 @@ func TestTRun(t *T) {
 		ok:   false,
 		output: `
 --- FAIL: subtest calls error on parent (N.NNs)
-	sub_test.go:NNN: first this
-	sub_test.go:NNN: and now this!
-	sub_test.go:NNN: oh, and this too`,
+    sub_test.go:NNN: first this
+    sub_test.go:NNN: and now this!
+    sub_test.go:NNN: oh, and this too`,
 		maxPar: 1,
 		f: func(t *T) {
 			t.Errorf("first this")
@@ -337,10 +337,10 @@ func TestTRun(t *T) {
 		ok:   false,
 		output: `
 --- FAIL: subtest calls fatal on parent (N.NNs)
-	sub_test.go:NNN: first this
-	sub_test.go:NNN: and now this!
+    sub_test.go:NNN: first this
+    sub_test.go:NNN: and now this!
     --- FAIL: subtest calls fatal on parent/#00 (N.NNs)
-    	testing.go:NNN: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test`,
+        testing.go:NNN: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test`,
 		maxPar: 1,
 		f: func(t *T) {
 			outer := t
@@ -355,10 +355,10 @@ func TestTRun(t *T) {
 		ok:   false,
 		output: `
 --- FAIL: subtest calls error on ancestor (N.NNs)
-	sub_test.go:NNN: Report to ancestor
+    sub_test.go:NNN: Report to ancestor
     --- FAIL: subtest calls error on ancestor/#00 (N.NNs)
-    	sub_test.go:NNN: Still do this
-	sub_test.go:NNN: Also do this`,
+        sub_test.go:NNN: Still do this
+    sub_test.go:NNN: Also do this`,
 		maxPar: 1,
 		f: func(t *T) {
 			outer := t
@@ -375,7 +375,7 @@ func TestTRun(t *T) {
 		ok:   false,
 		output: `
 --- FAIL: subtest calls fatal on ancestor (N.NNs)
-	sub_test.go:NNN: Nope`,
+    sub_test.go:NNN: Nope`,
 		maxPar: 1,
 		f: func(t *T) {
 			outer := t
@@ -503,7 +503,7 @@ func TestBRun(t *T) {
 		chatty: true,
 		output: `
 --- SKIP: root
-	sub_test.go:NNN: skipping`,
+    sub_test.go:NNN: skipping`,
 		f: func(b *B) { b.Skip("skipping") },
 	}, {
 		desc:   "chatty with recursion",
@@ -521,8 +521,8 @@ func TestBRun(t *T) {
 		failed: true,
 		output: `
 --- FAIL: root
-	sub_test.go:NNN: an error
-	sub_test.go:NNN: skipped`,
+    sub_test.go:NNN: an error
+    sub_test.go:NNN: skipped`,
 		f: func(b *B) {
 			b.Error("an error")
 			b.Skip("skipped")

src/testing/testing.go

@@ -394,7 +394,7 @@ func (c *common) frameSkip(skip int) runtime.Frame {
 }
 
 // decorate prefixes the string with the file and line of the call site
-// and inserts the final newline if needed and indentation tabs for formatting.
+// and inserts the final newline if needed and indentation spaces for formatting.
 // This function must be called with c.mu held.
 func (c *common) decorate(s string) string {
 	frame := c.frameSkip(3) // decorate + log + public function.
@@ -414,8 +414,8 @@ func (c *common) decorate(s string) string {
 		line = 1
 	}
 	buf := new(strings.Builder)
-	// Every line is indented at least one tab.
-	buf.WriteByte('\t')
+	// Every line is indented at least 4 spaces.
+	buf.WriteString("    ")
 	fmt.Fprintf(buf, "%s:%d: ", file, line)
 	lines := strings.Split(s, "\n")
 	if l := len(lines); l > 1 && lines[l-1] == "" {
@@ -423,8 +423,8 @@ func (c *common) decorate(s string) string {
 	}
 	for i, line := range lines {
 		if i > 0 {
-			// Second and subsequent lines are indented an extra tab.
-			buf.WriteString("\n\t\t")
+			// Second and subsequent lines are indented an additional 4 spaces.
+			buf.WriteString("\n        ")
 		}
 		buf.WriteString(line)
 	}