discovery: Improve Erlang service name heuristics (#42406)

### What does this PR do?
[DSCVR-237](https://datadoghq.atlassian.net/browse/DSCVR-237)

This PR improves the Erlang service name which was implemented in other [PR](#42322). The changes are the following: 

- Removed concatenated flag support (e.g., -prognameerl).
- Return empty string: Changed detectErlangAppName() to return "" instead of "beam" when no name can be extracted.
- Added 4 test cases in service_test.go to verify detector is properly hooked up (CouchDB, RabbitMQ, Riak, fallback)
- Code cleanup: Removed invalid tests, simplified logic.

### Motivation

Improve the heuristics that have already been implemented.

### Describe how you validated your changes
Testing locally.

### Additional Notes


[DSCVR-237]: https://datadoghq.atlassian.net/browse/DSCVR-237?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Co-authored-by: marta.vicentenavarro <[email protected]>

Author: martavicentenavarro

pkg/collector/corechecks/servicediscovery/usm/erlang.go

@@ -20,7 +20,7 @@ func newErlangDetector(ctx DetectionContext) detector {
 
 func (e erlangDetector) detect(args []string) (ServiceMetadata, bool) {
 	name := detectErlangAppName(args)
-	if name != "" && name != "beam" {
+	if name != "" {
 		return NewServiceMetadata(name, CommandLine), true
 	}
 	return ServiceMetadata{}, false
@@ -31,7 +31,7 @@ func detectErlangAppName(cmdline []string) string {
 	var home string
 
 	// Parse command line looking for -progname and -home flags.
-	// We support both separated (-progname erl) and concatenated (-prognameerl) forms.
+	// Erlang uses space-separated flag values (e.g., -progname erl).
 	for i := 0; i < len(cmdline); i++ {
 		arg := cmdline[i]
 
@@ -42,41 +42,29 @@ func detectErlangAppName(cmdline []string) string {
 			continue
 		}
 
-		// Check for -progname with concatenated value (e.g., -prognameerl)
-		if strings.HasPrefix(arg, "-progname") && len(arg) > 9 {
-			progname = strings.TrimSpace(arg[9:])
-			continue
-		}
-
 		// Check for -home flag (with value in next arg)
 		if arg == "-home" && i+1 < len(cmdline) {
 			home = strings.TrimSpace(cmdline[i+1])
 			i++
 			continue
 		}
-
-		// Check for -home with concatenated value (e.g., -home/var/lib/rabbitmq)
-		if strings.HasPrefix(arg, "-home") && len(arg) > 5 {
-			home = strings.TrimSpace(arg[5:])
-			continue
-		}
 	}
 
 	// Apply heuristics according to requirements.
-	// Compare progname case-insensitively to handle edge cases.
-	if progname != "" && !strings.EqualFold(progname, "erl") {
+	// Use exact comparison for progname
+	if progname != "" && progname != "erl" {
 		return progname
 	}
 
 	// Only use home if progname is explicitly "erl"
-	if strings.EqualFold(progname, "erl") && home != "" {
+	if progname == "erl" && home != "" {
 		// Extract the last component of the home path
 		base := filepath.Base(home)
 		if base != "" && base != "." && base != "/" {
 			return base
 		}
 	}
 
-	// Fallback to "beam"
-	return "beam"
+	// Return empty string to indicate we couldn't extract a name
+	return ""
 }

pkg/collector/corechecks/servicediscovery/usm/erlang_test.go

@@ -64,12 +64,12 @@ func Test_detectErlangAppName(t *testing.T) {
 			expected: "myapp",
 		},
 		{
-			name: "Fallback to beam when no progname or home",
+			name: "No progname or home returns empty string",
 			cmdline: []string{
 				"-smp", "auto",
 				"-noinput",
 			},
-			expected: "beam",
+			expected: "",
 		},
 		{
 			name: "Progname without home",
@@ -82,15 +82,15 @@ func Test_detectErlangAppName(t *testing.T) {
 		{
 			name:     "Empty command line",
 			cmdline:  []string{},
-			expected: "beam",
+			expected: "",
 		},
 		{
 			name: "Only home, no progname",
 			cmdline: []string{
 				"-home", "/opt/customapp",
 				"-noshell",
 			},
-			expected: "beam",
+			expected: "",
 		},
 		{
 			name: "Home with trailing slash",
@@ -156,31 +156,6 @@ func Test_detectErlangAppName(t *testing.T) {
 			},
 			expected: "couchdb",
 		},
-		{
-			name: "Progname concatenated without space",
-			cmdline: []string{
-				"-root", "/usr/lib/erlang",
-				"-prognamecouchdb",
-				"-home", "/opt/couchdb",
-			},
-			expected: "couchdb",
-		},
-		{
-			name: "Home concatenated without space",
-			cmdline: []string{
-				"-progname", "erl",
-				"-home/var/lib/rabbitmq",
-			},
-			expected: "rabbitmq",
-		},
-		{
-			name: "Both flags concatenated",
-			cmdline: []string{
-				"-prognameerl",
-				"-home/var/lib/ejabberd",
-			},
-			expected: "ejabberd",
-		},
 		{
 			name: "Progname with spaces in value",
 			cmdline: []string{
@@ -197,20 +172,38 @@ func Test_detectErlangAppName(t *testing.T) {
 			expected: "rabbitmq",
 		},
 		{
-			name: "Case insensitive erl - uppercase ERL",
+			name: "Uppercase ERL is not treated as erl",
 			cmdline: []string{
 				"-progname", "ERL",
 				"-home", "/var/lib/rabbitmq",
 			},
-			expected: "rabbitmq",
+			expected: "ERL",
 		},
 		{
-			name: "Case insensitive erl - mixed case Erl",
+			name: "Mixed case Erl is not treated as erl",
 			cmdline: []string{
 				"-progname", "Erl",
 				"-home", "/var/lib/ejabberd",
 			},
-			expected: "ejabberd",
+			expected: "Erl",
+		},
+		{
+			name: "progname as last argument without value",
+			cmdline: []string{
+				"-root", "/usr/lib/erlang",
+				"-home", "/var/lib/myapp",
+				"-progname",
+			},
+			expected: "",
+		},
+		{
+			name: "home as last argument without value",
+			cmdline: []string{
+				"-root", "/usr/lib/erlang",
+				"-progname", "erl",
+				"-home",
+			},
+			expected: "",
 		},
 	}
 
@@ -251,7 +244,7 @@ func Test_erlangDetector(t *testing.T) {
 			expectedSource:  CommandLine,
 		},
 		{
-			name: "Fallback to beam returns false",
+			name: "No name extracted returns false",
 			args: []string{
 				"-smp", "auto",
 			},

pkg/collector/corechecks/servicediscovery/usm/service_test.go

@@ -607,6 +607,55 @@ func TestExtractServiceMetadata(t *testing.T) {
 			expectedGeneratedName:       "dotnet",
 			expectedGeneratedNameSource: CommandLine,
 		},
+		{
+			name: "Erlang beam.smp with CouchDB progname",
+			cmdline: []string{
+				"/usr/lib/erlang/erts-12.3/bin/beam.smp",
+				"--",
+				"-root", "/usr/lib/erlang",
+				"-progname", "couchdb",
+				"-home", "/opt/couchdb",
+			},
+			expectedGeneratedName:       "couchdb",
+			expectedGeneratedNameSource: CommandLine,
+		},
+		{
+			name: "Erlang beam with RabbitMQ (erl progname, use home)",
+			cmdline: []string{
+				"/usr/lib/erlang/erts-11.2/bin/beam",
+				"--",
+				"-W", "w",
+				"-K", "true",
+				"-A", "192",
+				"-progname", "erl",
+				"-home", "/var/lib/rabbitmq",
+			},
+			expectedGeneratedName:       "rabbitmq",
+			expectedGeneratedNameSource: CommandLine,
+		},
+		{
+			name: "Erlang beam.smp with Riak progname",
+			cmdline: []string{
+				"beam.smp",
+				"--",
+				"-root", "/usr/lib/erlang",
+				"-progname", "riak",
+				"-home", "/var/lib/riak",
+			},
+			expectedGeneratedName:       "riak",
+			expectedGeneratedNameSource: CommandLine,
+		},
+		{
+			name: "Erlang beam with no useful name",
+			cmdline: []string{
+				"beam",
+				"--",
+				"-smp", "auto",
+				"-noinput",
+			},
+			expectedGeneratedName:       "beam",
+			expectedGeneratedNameSource: CommandLine,
+		},
 		{
 			name: "PHP Laravel",
 			cmdline: []string{