[chore][cmd/builder] Improve missing replace statements test (open-te…

…lemetry#10196)

Updates `TestReplaceStatementsAreComplete` to check the modules used in
replace statements to ensure that their dependencies also have replace
statements. This will catch the error that happened in open-telemetry#10188 before a
release is started.

The one caveat here is that the test may need to be run multiple times
if there are modules deep in the dependency tree that haven't been added
to the list of replace statement modules. In essence, the user has to do
a BFS walk of the dependency tree themselves by running the tests until
all missing modules are caught. We could automate this process with
additional code to report all missing modules at once regardless of
depth, but I figure it's not worth the extra complexity in the test for
such a small gain.

#### Testing

I tested this on the open-telemetry#10188 branch by removing the `pdata/testdata`
module from the replace statements list and seeing that the failure is
easier to understand:

```
--- FAIL: TestReplaceStatementsAreComplete (0.60s)
        	Error:      	Should be true
        	Test:       	TestReplaceStatementsAreComplete
        	Messages:   	Module missing from replace statements list: go.opentelemetry.io/collector/pdata/testdata
```

cmd/builder/internal/builder/main_test.go

@@ -341,6 +341,17 @@ func TestGenerateAndCompile(t *testing.T) {
 // local copy, `go get` will try to fetch the unreleased
 // version remotely and some tests will fail.
 func TestReplaceStatementsAreComplete(t *testing.T) {
+	workspaceDir := getWorkspaceDir()
+	replaceMods := map[string]bool{}
+
+	for _, suffix := range replaceModules {
+		replaceMods[modulePrefix+suffix] = false
+	}
+
+	for _, mod := range replaceModules {
+		verifyGoMod(t, workspaceDir+mod, replaceMods)
+	}
+
 	var err error
 	dir := t.TempDir()
 	cfg := NewDefaultConfig()
@@ -401,6 +412,14 @@ func TestReplaceStatementsAreComplete(t *testing.T) {
 	err = GenerateAndCompile(cfg)
 	require.NoError(t, err)
 
+	verifyGoMod(t, dir, replaceMods)
+
+	for k, v := range replaceMods {
+		assert.Truef(t, v, "Module not used: %s", k)
+	}
+}
+
+func verifyGoMod(t *testing.T, dir string, replaceMods map[string]bool) {
 	gomodpath := path.Join(dir, "go.mod")
 	// #nosec G304 We control this path and generate the file inside, so we can assume it is safe.
 	gomod, err := os.ReadFile(gomodpath)
@@ -409,12 +428,6 @@ func TestReplaceStatementsAreComplete(t *testing.T) {
 	mod, err := modfile.Parse(gomodpath, gomod, nil)
 	require.NoError(t, err)
 
-	replaceMods := map[string]bool{}
-
-	for _, suffix := range replaceModules {
-		replaceMods[modulePrefix+suffix] = false
-	}
-
 	for _, req := range mod.Require {
 		if !strings.HasPrefix(req.Mod.Path, modulePrefix) {
 			continue
@@ -425,15 +438,6 @@ func TestReplaceStatementsAreComplete(t *testing.T) {
 
 		replaceMods[req.Mod.Path] = true
 	}
-
-	// those are modules that should be part of the replaces, but are not components
-	for _, unused := range []string{"/pdata/testdata"} {
-		replaceMods[modulePrefix+unused] = true
-	}
-
-	for k, v := range replaceMods {
-		assert.Truef(t, v, "Module not used: %s", k)
-	}
 }
 
 func makeModule(dir string, fileContents []byte) error {
@@ -454,10 +458,7 @@ func makeModule(dir string, fileContents []byte) error {
 }
 
 func generateReplaces() []string {
-	// This test is dependent on the current file structure.
-	// The goal is find the root of the repo so we can replace the root module.
-	_, thisFile, _, _ := runtime.Caller(0)
-	workspaceDir := filepath.Dir(filepath.Dir(filepath.Dir(filepath.Dir(filepath.Dir(thisFile)))))
+	workspaceDir := getWorkspaceDir()
 	modules := replaceModules
 	replaces := make([]string, len(modules))
 
@@ -467,3 +468,10 @@ func generateReplaces() []string {
 
 	return replaces
 }
+
+func getWorkspaceDir() string {
+	// This is dependent on the current file structure.
+	// The goal is find the root of the repo so we can replace the root module.
+	_, thisFile, _, _ := runtime.Caller(0)
+	return filepath.Dir(filepath.Dir(filepath.Dir(filepath.Dir(filepath.Dir(thisFile)))))
+}