cmd/go: in tests, don't assume that the 'git' binary is present

Add a helper-function to testenv to make these skips more ergonomic.
Also update a few existing skips in cmd/go/... to use it.

Updates #25300

Change-Id: I4205b4fb2b685dfac1cff3c999f954bff7b0f3c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/181538Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -1222,10 +1222,12 @@ func TestInternalCache(t *testing.T) {
 }
 
 func TestMoveGit(t *testing.T) {
+	testenv.MustHaveExecPath(t, "git")
 	testMove(t, "git", "rsc.io/pdf", "pdf", "rsc.io/pdf/.git/config")
 }
 
 func TestMoveHG(t *testing.T) {
+	testenv.MustHaveExecPath(t, "hg")
 	testMove(t, "hg", "vcs-test.golang.org/go/custom-hg-hello", "custom-hg-hello", "vcs-test.golang.org/go/custom-hg-hello/.hg/hgrc")
 }
 
@@ -1287,9 +1289,7 @@ func TestImportCycle(t *testing.T) {
 // cmd/go: custom import path checking should not apply to Go packages without import comment.
 func TestIssue10952(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
-	if _, err := exec.LookPath("git"); err != nil {
-		t.Skip("skipping because git binary not found")
-	}
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -1305,9 +1305,7 @@ func TestIssue10952(t *testing.T) {
 
 func TestIssue16471(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
-	if _, err := exec.LookPath("git"); err != nil {
-		t.Skip("skipping because git binary not found")
-	}
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -1323,9 +1321,7 @@ func TestIssue16471(t *testing.T) {
 // Test git clone URL that uses SCP-like syntax and custom import path checking.
 func TestIssue11457(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
-	if _, err := exec.LookPath("git"); err != nil {
-		t.Skip("skipping because git binary not found")
-	}
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -1350,9 +1346,7 @@ func TestIssue11457(t *testing.T) {
 
 func TestGetGitDefaultBranch(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
-	if _, err := exec.LookPath("git"); err != nil {
-		t.Skip("skipping because git binary not found")
-	}
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -1378,9 +1372,7 @@ func TestGetGitDefaultBranch(t *testing.T) {
 // Security issue. Don't disable. See golang.org/issue/22125.
 func TestAccidentalGitCheckout(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
-	if _, err := exec.LookPath("git"); err != nil {
-		t.Skip("skipping because git binary not found")
-	}
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -1653,6 +1645,7 @@ func TestInstallToGOBINCommandLinePackage(t *testing.T) {
 
 func TestGoGetNonPkg(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -1669,6 +1662,7 @@ func TestGoGetNonPkg(t *testing.T) {
 
 func TestGoGetTestOnlyPkg(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -2058,6 +2052,7 @@ func TestDefaultGOPATH(t *testing.T) {
 
 func TestDefaultGOPATHGet(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -2439,6 +2434,7 @@ func TestSymlinkWarning(t *testing.T) {
 // Issue 8181.
 func TestGoGetDashTIssue8181(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -2453,6 +2449,7 @@ func TestGoGetDashTIssue8181(t *testing.T) {
 func TestIssue11307(t *testing.T) {
 	// go get -u was not working except in checkout directory
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -2931,6 +2928,7 @@ func TestCgoPkgConfig(t *testing.T) {
 
 	tg.run("env", "PKG_CONFIG")
 	pkgConfig := strings.TrimSpace(tg.getStdout())
+	testenv.MustHaveExecPath(t, pkgConfig)
 	if out, err := exec.Command(pkgConfig, "--atleast-pkgconfig-version", "0.24").CombinedOutput(); err != nil {
 		t.Skipf("%s --atleast-pkgconfig-version 0.24: %v\n%s", pkgConfig, err, out)
 	}
@@ -3033,9 +3031,7 @@ func TestIssue7573(t *testing.T) {
 	if !canCgo {
 		t.Skip("skipping because cgo not enabled")
 	}
-	if _, err := exec.LookPath("gccgo"); err != nil {
-		t.Skip("skipping because no gccgo compiler found")
-	}
+	testenv.MustHaveExecPath(t, "gccgo")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3324,6 +3320,7 @@ func TestGoGenerateBadImports(t *testing.T) {
 
 func TestGoGetCustomDomainWildcard(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3335,6 +3332,7 @@ func TestGoGetCustomDomainWildcard(t *testing.T) {
 
 func TestGoGetInternalWildcard(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3407,6 +3405,7 @@ func TestVetWithOnlyCgoFiles(t *testing.T) {
 // Issue 9767, 19769.
 func TestGoGetDotSlashDownload(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3662,6 +3661,7 @@ func TestImportLocal(t *testing.T) {
 func TestGoGetInsecure(t *testing.T) {
 	test := func(t *testing.T, modules bool) {
 		testenv.MustHaveExternalNetwork(t)
+		testenv.MustHaveExecPath(t, "git")
 
 		tg := testgo(t)
 		defer tg.cleanup()
@@ -3702,6 +3702,7 @@ func TestGoGetInsecure(t *testing.T) {
 
 func TestGoGetUpdateInsecure(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3726,6 +3727,7 @@ func TestGoGetUpdateInsecure(t *testing.T) {
 
 func TestGoGetUpdateUnknownProtocol(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3760,6 +3762,7 @@ func TestGoGetUpdateUnknownProtocol(t *testing.T) {
 
 func TestGoGetInsecureCustomDomain(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3862,6 +3865,7 @@ func TestGoGetUpdate(t *testing.T) {
 	// former dependencies, not current ones.
 
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -3889,6 +3893,7 @@ func TestGoGetUpdate(t *testing.T) {
 // Issue #20512.
 func TestGoGetRace(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 	if !canRace {
 		t.Skip("skipping because race detector not supported")
 	}
@@ -3905,6 +3910,7 @@ func TestGoGetDomainRoot(t *testing.T) {
 	// go get foo.io (not foo.io/subdir) was not working consistently.
 
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -4295,6 +4301,7 @@ func TestGenerateUsesBuildContext(t *testing.T) {
 // Issue 14450: go get -u .../ tried to import not downloaded package
 func TestGoGetUpdateWithWildcard(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -5043,9 +5050,8 @@ func TestExecBuildX(t *testing.T) {
 		t.Skip("skipping because cgo not enabled")
 	}
 
-	if runtime.GOOS == "plan9" || runtime.GOOS == "windows" {
-		t.Skipf("skipping because unix shell is not supported on %s", runtime.GOOS)
-	}
+	testenv.MustHaveExecPath(t, "/usr/bin/env")
+	testenv.MustHaveExecPath(t, "bash")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -5126,9 +5132,10 @@ func TestUpxCompression(t *testing.T) {
 		t.Skipf("skipping upx test on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 
+	testenv.MustHaveExecPath(t, "upx")
 	out, err := exec.Command("upx", "--version").CombinedOutput()
 	if err != nil {
-		t.Skip("skipping because upx is not available")
+		t.Fatalf("upx --version failed: %v", err)
 	}
 
 	// upx --version prints `upx <version>` in the first line of output:
@@ -5137,13 +5144,13 @@ func TestUpxCompression(t *testing.T) {
 	re := regexp.MustCompile(`([[:digit:]]+)\.([[:digit:]]+)`)
 	upxVersion := re.FindStringSubmatch(string(out))
 	if len(upxVersion) != 3 {
-		t.Errorf("bad upx version string: %s", upxVersion)
+		t.Fatalf("bad upx version string: %s", upxVersion)
 	}
 
 	major, err1 := strconv.Atoi(upxVersion[1])
 	minor, err2 := strconv.Atoi(upxVersion[2])
 	if err1 != nil || err2 != nil {
-		t.Errorf("bad upx version string: %s", upxVersion[0])
+		t.Fatalf("bad upx version string: %s", upxVersion[0])
 	}
 
 	// Anything below 3.94 is known not to work with go binaries
@@ -5196,26 +5203,29 @@ func TestQEMUUserMode(t *testing.T) {
 	src, obj := tg.path("main.go"), tg.path("main")
 
 	for _, arch := range testArchs {
-		out, err := exec.Command("qemu-"+arch.qemu, "--version").CombinedOutput()
-		if err != nil {
-			t.Logf("Skipping %s test (qemu-%s not available)", arch.g, arch.qemu)
-			continue
-		}
+		arch := arch
+		t.Run(arch.g, func(t *testing.T) {
+			qemu := "qemu-" + arch.qemu
+			testenv.MustHaveExecPath(t, qemu)
+
+			out, err := exec.Command(qemu, "--version").CombinedOutput()
+			if err != nil {
+				t.Fatalf("%s --version failed: %v", qemu, err)
+			}
 
-		tg.setenv("GOARCH", arch.g)
-		tg.run("build", "-o", obj, src)
+			tg.setenv("GOARCH", arch.g)
+			tg.run("build", "-o", obj, src)
 
-		out, err = exec.Command("qemu-"+arch.qemu, obj).CombinedOutput()
-		if err != nil {
-			t.Logf("qemu-%s output:\n%s\n", arch.qemu, out)
-			t.Errorf("qemu-%s failed with %v", arch.qemu, err)
-			continue
-		}
-		if want := "hello qemu-user"; string(out) != want {
-			t.Errorf("bad output from qemu-%s:\ngot %s; want %s", arch.qemu, out, want)
-		}
+			out, err = exec.Command(qemu, obj).CombinedOutput()
+			if err != nil {
+				t.Logf("%s output:\n%s\n", qemu, out)
+				t.Fatalf("%s failed with %v", qemu, err)
+			}
+			if want := "hello qemu-user"; string(out) != want {
+				t.Errorf("bad output from %s:\ngot %s; want %s", qemu, out, want)
+			}
+		})
 	}
-
 }
 
 func TestCacheListStale(t *testing.T) {

src/cmd/go/internal/modfetch/coderepo_test.go

@@ -48,11 +48,12 @@ const (
 	vgotest1hg  = "vcs-test.golang.org/hg/vgotest1.hg"
 )
 
-var altVgotests = []string{
-	vgotest1hg,
+var altVgotests = map[string]string{
+	"hg": vgotest1hg,
 }
 
 type codeRepoTest struct {
+	vcs      string
 	path     string
 	lookerr  string
 	mpath    string
@@ -70,6 +71,7 @@ type codeRepoTest struct {
 
 var codeRepoTests = []codeRepoTest{
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1",
 		rev:     "v0.0.0",
 		version: "v0.0.0",
@@ -83,6 +85,7 @@ var codeRepoTests = []codeRepoTest{
 		},
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1",
 		rev:     "v1.0.0",
 		version: "v1.0.0",
@@ -96,6 +99,7 @@ var codeRepoTests = []codeRepoTest{
 		},
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1/v2",
 		rev:     "v2.0.0",
 		version: "v2.0.0",
@@ -105,6 +109,7 @@ var codeRepoTests = []codeRepoTest{
 		ziperr:  "missing github.com/rsc/vgotest1/go.mod and .../v2/go.mod at revision v2.0.0",
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1",
 		rev:     "80d85c5",
 		version: "v1.0.0",
@@ -118,6 +123,7 @@ var codeRepoTests = []codeRepoTest{
 		},
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1",
 		rev:     "mytag",
 		version: "v1.0.0",
@@ -131,6 +137,7 @@ var codeRepoTests = []codeRepoTest{
 		},
 	},
 	{
+		vcs:      "git",
 		path:     "github.com/rsc/vgotest1/v2",
 		rev:      "45f53230a",
 		version:  "v2.0.0",
@@ -141,6 +148,7 @@ var codeRepoTests = []codeRepoTest{
 		ziperr:   "missing github.com/rsc/vgotest1/go.mod and .../v2/go.mod at revision v2.0.0",
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1/v54321",
 		rev:     "80d85c5",
 		version: "v54321.0.0-20180219231006-80d85c5d4d17",
@@ -150,16 +158,19 @@ var codeRepoTests = []codeRepoTest{
 		ziperr:  "missing github.com/rsc/vgotest1/go.mod and .../v54321/go.mod at revision 80d85c5d4d17",
 	},
 	{
+		vcs:  "git",
 		path: "github.com/rsc/vgotest1/submod",
 		rev:  "v1.0.0",
 		err:  "unknown revision submod/v1.0.0",
 	},
 	{
+		vcs:  "git",
 		path: "github.com/rsc/vgotest1/submod",
 		rev:  "v1.0.3",
 		err:  "unknown revision submod/v1.0.3",
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1/submod",
 		rev:     "v1.0.4",
 		version: "v1.0.4",
@@ -174,6 +185,7 @@ var codeRepoTests = []codeRepoTest{
 		},
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1",
 		rev:     "v1.1.0",
 		version: "v1.1.0",
@@ -189,6 +201,7 @@ var codeRepoTests = []codeRepoTest{
 		},
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1/v2",
 		rev:     "v2.0.1",
 		version: "v2.0.1",
@@ -198,6 +211,7 @@ var codeRepoTests = []codeRepoTest{
 		gomod:   "module \"github.com/rsc/vgotest1/v2\" // root go.mod\n",
 	},
 	{
+		vcs:      "git",
 		path:     "github.com/rsc/vgotest1/v2",
 		rev:      "v2.0.3",
 		version:  "v2.0.3",
@@ -207,6 +221,7 @@ var codeRepoTests = []codeRepoTest{
 		gomoderr: "github.com/rsc/vgotest1/v2/go.mod has non-.../v2 module path \"github.com/rsc/vgotest\" at revision v2.0.3",
 	},
 	{
+		vcs:      "git",
 		path:     "github.com/rsc/vgotest1/v2",
 		rev:      "v2.0.4",
 		version:  "v2.0.4",
@@ -216,6 +231,7 @@ var codeRepoTests = []codeRepoTest{
 		gomoderr: "github.com/rsc/vgotest1/go.mod and .../v2/go.mod both have .../v2 module paths at revision v2.0.4",
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1/v2",
 		rev:     "v2.0.5",
 		version: "v2.0.5",
@@ -226,6 +242,7 @@ var codeRepoTests = []codeRepoTest{
 	},
 	{
 		// redirect to github
+		vcs:     "git",
 		path:    "rsc.io/quote",
 		rev:     "v1.0.0",
 		version: "v1.0.0",
@@ -236,6 +253,7 @@ var codeRepoTests = []codeRepoTest{
 	},
 	{
 		// redirect to static hosting proxy
+		vcs:     "mod",
 		path:    "swtch.com/testmod",
 		rev:     "v1.0.0",
 		version: "v1.0.0",
@@ -245,6 +263,7 @@ var codeRepoTests = []codeRepoTest{
 	},
 	{
 		// redirect to googlesource
+		vcs:     "git",
 		path:    "golang.org/x/text",
 		rev:     "4e4a3210bb",
 		version: "v0.3.1-0.20180208041248-4e4a3210bb54",
@@ -253,6 +272,7 @@ var codeRepoTests = []codeRepoTest{
 		time:    time.Date(2018, 2, 8, 4, 12, 48, 0, time.UTC),
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/pkg/errors",
 		rev:     "v0.8.0",
 		version: "v0.8.0",
@@ -264,17 +284,20 @@ var codeRepoTests = []codeRepoTest{
 		// package in subdirectory - custom domain
 		// In general we can't reject these definitively in Lookup,
 		// but gopkg.in is special.
+		vcs:     "git",
 		path:    "gopkg.in/yaml.v2/abc",
 		lookerr: "invalid module path \"gopkg.in/yaml.v2/abc\"",
 	},
 	{
 		// package in subdirectory - github
 		// Because it's a package, Stat should fail entirely.
+		vcs:  "git",
 		path: "github.com/rsc/quote/buggy",
 		rev:  "c4d4236f",
 		err:  "missing github.com/rsc/quote/buggy/go.mod at revision c4d4236f9242",
 	},
 	{
+		vcs:     "git",
 		path:    "gopkg.in/yaml.v2",
 		rev:     "d670f940",
 		version: "v2.0.0",
@@ -284,6 +307,7 @@ var codeRepoTests = []codeRepoTest{
 		gomod:   "module gopkg.in/yaml.v2\n",
 	},
 	{
+		vcs:     "git",
 		path:    "gopkg.in/check.v1",
 		rev:     "20d25e280405",
 		version: "v1.0.0-20161208181325-20d25e280405",
@@ -293,6 +317,7 @@ var codeRepoTests = []codeRepoTest{
 		gomod:   "module gopkg.in/check.v1\n",
 	},
 	{
+		vcs:     "git",
 		path:    "gopkg.in/yaml.v2",
 		rev:     "v2",
 		version: "v2.2.3-0.20190319135612-7b8349ac747c",
@@ -302,6 +327,7 @@ var codeRepoTests = []codeRepoTest{
 		gomod:   "module \"gopkg.in/yaml.v2\"\n\nrequire (\n\t\"gopkg.in/check.v1\" v0.0.0-20161208181325-20d25e280405\n)\n",
 	},
 	{
+		vcs:     "git",
 		path:    "vcs-test.golang.org/go/mod/gitrepo1",
 		rev:     "master",
 		version: "v1.2.4-annotated",
@@ -311,6 +337,7 @@ var codeRepoTests = []codeRepoTest{
 		gomod:   "module vcs-test.golang.org/go/mod/gitrepo1\n",
 	},
 	{
+		vcs:     "git",
 		path:    "gopkg.in/natefinch/lumberjack.v2",
 		rev:     "latest",
 		version: "v2.0.0-20170531160350-a96e63847dc3",
@@ -320,6 +347,7 @@ var codeRepoTests = []codeRepoTest{
 		gomod:   "module gopkg.in/natefinch/lumberjack.v2\n",
 	},
 	{
+		vcs:  "git",
 		path: "gopkg.in/natefinch/lumberjack.v2",
 		// This repo has a v2.1 tag.
 		// We only allow semver references to tags that are fully qualified, as in v2.1.0.
@@ -335,6 +363,7 @@ var codeRepoTests = []codeRepoTest{
 		gomod:   "module gopkg.in/natefinch/lumberjack.v2\n",
 	},
 	{
+		vcs:     "git",
 		path:    "vcs-test.golang.org/go/v2module/v2",
 		rev:     "v2.0.0",
 		version: "v2.0.0",
@@ -359,6 +388,9 @@ func TestCodeRepo(t *testing.T) {
 			f := func(tt codeRepoTest) func(t *testing.T) {
 				return func(t *testing.T) {
 					t.Parallel()
+					if tt.vcs != "mod" {
+						testenv.MustHaveExecPath(t, tt.vcs)
+					}
 
 					repo, err := Lookup("direct", tt.path)
 					if tt.lookerr != "" {
@@ -457,9 +489,10 @@ func TestCodeRepo(t *testing.T) {
 			}
 			t.Run(strings.ReplaceAll(tt.path, "/", "_")+"/"+tt.rev, f(tt))
 			if strings.HasPrefix(tt.path, vgotest1git) {
-				for _, alt := range altVgotests {
+				for vcs, alt := range altVgotests {
 					// Note: Communicating with f through tt; should be cleaned up.
 					old := tt
+					tt.vcs = vcs
 					tt.path = alt + strings.TrimPrefix(tt.path, vgotest1git)
 					if strings.HasPrefix(tt.mpath, vgotest1git) {
 						tt.mpath = alt + strings.TrimPrefix(tt.mpath, vgotest1git)
@@ -515,32 +548,39 @@ func remap(name string, m map[string]string) string {
 }
 
 var codeRepoVersionsTests = []struct {
+	vcs      string
 	path     string
 	prefix   string
 	versions []string
 }{
 	{
+		vcs:      "git",
 		path:     "github.com/rsc/vgotest1",
 		versions: []string{"v0.0.0", "v0.0.1", "v1.0.0", "v1.0.1", "v1.0.2", "v1.0.3", "v1.1.0", "v2.0.0+incompatible"},
 	},
 	{
+		vcs:      "git",
 		path:     "github.com/rsc/vgotest1",
 		prefix:   "v1.0",
 		versions: []string{"v1.0.0", "v1.0.1", "v1.0.2", "v1.0.3"},
 	},
 	{
+		vcs:      "git",
 		path:     "github.com/rsc/vgotest1/v2",
 		versions: []string{"v2.0.0", "v2.0.1", "v2.0.2", "v2.0.3", "v2.0.4", "v2.0.5", "v2.0.6"},
 	},
 	{
+		vcs:      "mod",
 		path:     "swtch.com/testmod",
 		versions: []string{"v1.0.0", "v1.1.1"},
 	},
 	{
+		vcs:      "git",
 		path:     "gopkg.in/russross/blackfriday.v2",
 		versions: []string{"v2.0.0", "v2.0.1"},
 	},
 	{
+		vcs:      "git",
 		path:     "gopkg.in/natefinch/lumberjack.v2",
 		versions: []string{"v2.0.0"},
 	},
@@ -560,6 +600,9 @@ func TestCodeRepoVersions(t *testing.T) {
 			t.Run(strings.ReplaceAll(tt.path, "/", "_"), func(t *testing.T) {
 				tt := tt
 				t.Parallel()
+				if tt.vcs != "mod" {
+					testenv.MustHaveExecPath(t, tt.vcs)
+				}
 
 				repo, err := Lookup("direct", tt.path)
 				if err != nil {
@@ -578,23 +621,28 @@ func TestCodeRepoVersions(t *testing.T) {
 }
 
 var latestTests = []struct {
+	vcs     string
 	path    string
 	version string
 	err     string
 }{
 	{
+		vcs:  "git",
 		path: "github.com/rsc/empty",
 		err:  "no commits",
 	},
 	{
+		vcs:     "git",
 		path:    "github.com/rsc/vgotest1",
 		version: "v0.0.0-20180219223237-a08abb797a67",
 	},
 	{
+		vcs:  "git",
 		path: "github.com/rsc/vgotest1/subdir",
 		err:  "missing github.com/rsc/vgotest1/subdir/go.mod at revision a08abb797a67",
 	},
 	{
+		vcs:     "mod",
 		path:    "swtch.com/testmod",
 		version: "v1.1.1",
 	},
@@ -615,6 +663,9 @@ func TestLatest(t *testing.T) {
 			t.Run(name, func(t *testing.T) {
 				tt := tt
 				t.Parallel()
+				if tt.vcs != "mod" {
+					testenv.MustHaveExecPath(t, tt.vcs)
+				}
 
 				repo, err := Lookup("direct", tt.path)
 				if err != nil {

src/cmd/go/internal/modload/import_test.go

@@ -43,6 +43,7 @@ var importTests = []struct {
 
 func TestImport(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	for _, tt := range importTests {
 		t.Run(strings.ReplaceAll(tt.path, "/", "_"), func(t *testing.T) {

src/cmd/go/internal/modload/query_test.go

@@ -136,6 +136,7 @@ var queryTests = []struct {
 
 func TestQuery(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	for _, tt := range queryTests {
 		allow := tt.allow

src/cmd/go/testdata/script/get_404_meta.txt

 # golang.org/issue/13037: 'go get' was not parsing <meta> tags in 404 served over HTTPS.
 
 [!net] skip
+[!exec:git] skip
 
 env GO111MODULE=off
 go get -d -insecure bazil.org/fuse/fs/fstestutil

src/cmd/go/testdata/script/get_insecure_redirect.txt

 # golang.org/issue/29591: 'go get' was following plain-HTTP redirects even without -insecure.
 
 [!net] skip
+[!exec:git] skip
 
 env GO111MODULE=on
 env GOPROXY=direct

src/cmd/go/testdata/script/mod_get_hash.txt

@@ -2,6 +2,7 @@ env GO111MODULE=on
 env GOPROXY=direct
 env GOSUMDB=off
 [!net] skip
+[!exec:git] skip
 
 # fetch commit hash reachable from refs/heads/* and refs/tags/* is OK
 go list -m golang.org/x/time@8be79e1e0910c292df4e79c241bb7e8f7e725959 # on master branch
@@ -16,4 +17,3 @@ stderr 'unknown revision'
 
 -- go.mod --
 module m
-

src/cmd/go/testdata/script/mod_gonoproxy.txt

@@ -16,6 +16,7 @@ go get rsc.io/quote
 
 # and GONOPROXY bypasses proxy
 [!net] skip
+[!exec:git] skip
 env GONOPROXY='*/fortune'
 ! go get rsc.io/fortune # does not exist in real world, only on test proxy
 stderr 'git ls-remote'

src/cmd/go/testdata/script/mod_gopkg_unstable.txt

@@ -8,6 +8,7 @@ cp go.mod.empty go.mod
 go list
 
 [!net] skip
+[!exec:git] skip
 
 env GOPROXY=direct
 env GOSUMDB=off

src/cmd/go/testdata/script/mod_sumdb_golang.txt

@@ -11,6 +11,7 @@ stdout '^sum.golang.org$'
 
 # download direct from github
 [!net] skip
+[!exec:git] skip
 env GOSUMDB=sum.golang.org
 env GOPROXY=direct
 go get -d rsc.io/quote

src/cmd/go/vendor_test.go

@@ -181,6 +181,7 @@ func TestVendorGet(t *testing.T) {
 
 func TestVendorGetUpdate(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -192,6 +193,7 @@ func TestVendorGetUpdate(t *testing.T) {
 
 func TestVendorGetU(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -202,6 +204,7 @@ func TestVendorGetU(t *testing.T) {
 
 func TestVendorGetTU(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -212,6 +215,7 @@ func TestVendorGetTU(t *testing.T) {
 
 func TestVendorGetBadVendor(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	for _, suffix := range []string{"bad/imp", "bad/imp2", "bad/imp3", "..."} {
 		t.Run(suffix, func(t *testing.T) {
@@ -228,6 +232,7 @@ func TestVendorGetBadVendor(t *testing.T) {
 
 func TestGetSubmodules(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -248,6 +253,7 @@ func TestVendorCache(t *testing.T) {
 
 func TestVendorTest2(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -273,6 +279,7 @@ func TestVendorTest2(t *testing.T) {
 
 func TestVendorTest3(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -299,6 +306,7 @@ func TestVendorTest3(t *testing.T) {
 
 func TestVendorList(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()
@@ -349,6 +357,7 @@ func TestLegacyMod(t *testing.T) {
 
 func TestLegacyModGet(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
+	testenv.MustHaveExecPath(t, "git")
 
 	tg := testgo(t)
 	defer tg.cleanup()

src/internal/testenv/testenv.go

@@ -19,6 +19,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 )
 
@@ -146,6 +147,24 @@ func MustHaveExec(t testing.TB) {
 	}
 }
 
+var execPaths sync.Map // path -> error
+
+// MustHaveExecPath checks that the current system can start the named executable
+// using os.StartProcess or (more commonly) exec.Command.
+// If not, MustHaveExecPath calls t.Skip with an explanation.
+func MustHaveExecPath(t testing.TB, path string) {
+	MustHaveExec(t)
+
+	err, found := execPaths.Load(path)
+	if !found {
+		_, err = exec.LookPath(path)
+		err, _ = execPaths.LoadOrStore(path, err)
+	}
+	if err != nil {
+		t.Skipf("skipping test: %s: %s", path, err)
+	}
+}
+
 // HasExternalNetwork reports whether the current system can use
 // external (non-localhost) networks.
 func HasExternalNetwork() bool {