What version of Go are you using (go version)?

$ go version
go version devel +c20b71eb37 Sat Nov 16 02:06:39 2019 +0000 linux/amd6

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

$ go env
GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/home/u/.cache/go-build"

GOENV="/home/u/.config/go/env"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOINSECURE=""

GONOPROXY=""

GONOSUMDB=""

GOOS="linux"

GOPATH="/home/u/goget:/home/u/Desktop/go"

GOPRIVATE=""

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/home/u/go"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/home/u/go/pkg/tool/linux_amd64"

GCCGO="gccgo"

AR="ar"

CC="gcc"

CXX="g++"

CGO_ENABLED="1"

GOMOD="/home/u/go/src/cmd/go.mod"

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build745246669=/tmp/go-build -gno-record-gcc-switches"

What did you do?

1. clone the go repository: git clone https://go.googlesource.com/go.git
2. build go as usual: cd src; ./all.bash
3. edit cmd/fix/context_test.go to ensure that the test case should FAIL.

diff --git a/src/cmd/fix/context_test.go b/src/cmd/fix/context_test.go
index 935d0d7235..f666be2fb1 100644
--- a/src/cmd/fix/context_test.go
+++ b/src/cmd/fix/context_test.go
@@ -19,7 +19,7 @@ var _ = "golang.org/x/net/context"
 `,
                Out: `package main
 
-import "context"
+import "context"x
 
 var _ = "golang.org/x/net/context"
 `,

4. run go test from the src/cmd/fix directory.

$ go test
PASS
ok  	cmd/fix	0.032s

5. notice that the test case passes, even though it should fail, given that we edited the expected output of the context rewrite rule.

6. remove call to t.Parallel in cmd/fix/main_test.go

diff --git a/src/cmd/fix/main_test.go b/src/cmd/fix/main_test.go
index ee74f24c6e..5214d67af1 100644
--- a/src/cmd/fix/main_test.go
+++ b/src/cmd/fix/main_test.go
@@ -77,7 +77,7 @@ func parseFixPrint(t *testing.T, fn func(*ast.File) bool, desc, in string, mustB
 func TestRewrite(t *testing.T) {
        for _, tt := range testCases {
                t.Run(tt.Name, func(t *testing.T) {
-                       t.Parallel()
+                       //t.Parallel()
                        // Apply fix: should get tt.Out.
                        out, fixed, ok := parseFixPrint(t, tt.Fn, tt.Name, tt.In, true)
                        if !ok {

7. re-run test case using go test from the src/cmd/fix directory.

--- FAIL: TestRewrite (2.86s)
    --- FAIL: TestRewrite/context.0 (0.00s)
        main_test.go:94: incorrect output.
        main_test.go:96: --- have
            package main
            
            import "context"
            
            var _ = "golang.org/x/net/context"
            
            --- want
            package main
            
            import "context"x
            
            var _ = "golang.org/x/net/context"
        main_test.go:133: --- /tmp/go-fix-test929058818	2019-11-15 21:39:47.643666701 -0600
            +++ /tmp/go-fix-test221839737	2019-11-15 21:39:47.643666701 -0600
            @@ -1,5 +1,5 @@
             package main
             
            -import "context"
            +import "context"x
             
             var _ = "golang.org/x/net/context"
            
FAIL
exit status 1
FAIL	cmd/fix	2.866s

8. notice that the test case now fails, as it should do, given that we edited the expected output of the context rewrite rule.

What did you expect to see?

A failed test case (after having modified the expected output of the context_test.go test case).

What did you see instead?

Test cases passing without error.