cmd/go/internal/imports: remove test dependency on json internals

TestScan loads encoding/json and verifies that various imports
match expectations. The new v2 encoding/json violates these
expectations. Since this test is testing the ScanDir function,
not encoding/json, change it to use a test package with defined
imports instead.

Change-Id: I68a0813ccf37daadbd6ea52872a8ac132141e82a
Reviewed-on: https://go-review.googlesource.com/c/go/+/665795
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Bypass: Damien Neil <dneil@google.com>
Auto-Submit: Damien Neil <dneil@google.com>

src/cmd/go/internal/imports/scan_test.go

@@ -17,26 +17,26 @@ import (
 func TestScan(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 
-	imports, testImports, err := ScanDir(filepath.Join(testenv.GOROOT(t), "src/encoding/json"), Tags())
+	imports, testImports, err := ScanDir(filepath.Join(testenv.GOROOT(t), "src/cmd/go/internal/imports/testdata/test"), Tags())
 	if err != nil {
 		t.Fatal(err)
 	}
-	foundBase64 := false
+	foundFmt := false
 	for _, p := range imports {
-		if p == "encoding/base64" {
-			foundBase64 = true
+		if p == "fmt" {
+			foundFmt = true // test package imports fmt directly
 		}
 		if p == "encoding/binary" {
 			// A dependency but not an import
-			t.Errorf("json reported as importing encoding/binary but does not")
+			t.Errorf("testdata/test reported as importing encoding/binary but does not")
 		}
 		if p == "net/http" {
 			// A test import but not an import
-			t.Errorf("json reported as importing net/http but does not")
+			t.Errorf("testdata/test reported as importing net/http but does not")
 		}
 	}
-	if !foundBase64 {
-		t.Errorf("json missing import encoding/base64 (%q)", imports)
+	if !foundFmt {
+		t.Errorf("testdata/test missing import fmt (%q)", imports)
 	}
 
 	foundHTTP := false
@@ -44,13 +44,13 @@ func TestScan(t *testing.T) {
 		if p == "net/http" {
 			foundHTTP = true
 		}
-		if p == "unicode/utf16" {
+		if p == "fmt" {
 			// A package import but not a test import
-			t.Errorf("json reported as test-importing unicode/utf16  but does not")
+			t.Errorf("testdata/test reported as test-importing fmt  but does not")
 		}
 	}
 	if !foundHTTP {
-		t.Errorf("json missing test import net/http (%q)", testImports)
+		t.Errorf("testdata/test missing test import net/http (%q)", testImports)
 	}
 }
 func TestScanDir(t *testing.T) {

src/cmd/go/internal/imports/testdata/test/child/child.go

@@ -0,0 +1,5 @@
+package child
+
+import "encoding/binary"
+
+var V = binary.MaxVarintLen16

src/cmd/go/internal/imports/testdata/test/test.go

@@ -0,0 +1,10 @@
+package test
+
+import (
+	"cmd/go/internal/imports/testdata/test/child"
+	"fmt"
+)
+
+func F() {
+	fmt.Println(child.V)
+}

src/cmd/go/internal/imports/testdata/test/test_test.go

@@ -0,0 +1,9 @@
+package test_test
+
+import (
+	_ "net/http"
+	"testing"
+)
+
+func Test(t *testing.T) {
+}

src/cmd/go/internal/imports/testdata/test/want.txt

@@ -0,0 +1,2 @@
+cmd/go/internal/imports/testdata/test/child
+fmt