added e2e, updated test & README

pkg/ottl/e2e/e2e_test.go

@@ -534,6 +534,36 @@ func Test_e2e_converters(t *testing.T) {
 				s.AppendEmpty().SetStr("C")
 			},
 		},
+		{
+			statement: `set(attributes["test"], String("test"))`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "test")
+			},
+		},
+		{
+			statement: `set(attributes["test"], String(attributes["http.method"]))`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "get")
+			},
+		},
+		{
+			statement: `set(attributes["test"], String(span_id))`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "[1,2,3,4,5,6,7,8]")
+			},
+		},
+		{
+			statement: `set(attributes["test"], String([1,2,3]))`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "[1,2,3]")
+			},
+		},
+		{
+			statement: `set(attributes["test"], String(true))`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "true")
+			},
+		},
 		{
 			statement: `set(attributes["test"], Substring("pass", 0, 2))`,
 			want: func(tCtx ottllog.TransformContext) {

pkg/ottl/ottlfuncs/README.md

@@ -1077,23 +1077,24 @@ The `String` Converter converts the `value` to string type.
 
 The returned type is `string`.
 
-- float64. The function returns the `value` as a string type.
-- string. The function returns the `value`, even if it's empty.
-- bool. The function returns true/false as "true"/"false".
-- int64. The function returns the `value` as a string type.
-- struct. The function returns an empty struct as "{}"
+- string. The function returns the `value` without changes.
+- []byte. The function returns the `value` as a string encoded in hexadecimal.
+- map. The function returns the `value` as a key-value-pair of type string.
+- slice. The function returns the `value` as a list formatted string.
+- pcommon.Value. The function returns the `value` as a string type.
 
-If value is empty, another type or parsing failed, nil is always returned.
+If `value` is of another type it gets marshalled to string type.
+If `value` is empty, or parsing failed, nil is always returned.
 
 The `value` is either a path expression to a telemetry field to retrieve, or a literal.
 
 Examples:
 
-- `String(2.7)`
-- `String("")`
+- `String("test")`
+- `String(attributes["http.method"])`
+- `String(span_id)`
+- `String([1,2,3])`
 - `String(false)`
-- `String(13)`
-- `String(attributes["http.status_code"])`
 
 ### Substring
 

pkg/ottl/ottlfuncs/func_string_test.go

@@ -65,10 +65,19 @@ func Test_String(t *testing.T) {
 			expected: nil,
 		},
 		{
-			name:     "some struct",
-			value:    struct{}{},
-			expected: "{}",
-			err:      false,
+			name:     "byte",
+			value:    []byte{123},
+			expected: string("7b"),
+		},
+		{
+			name:     "map",
+			value:    map[int]bool{1: true, 2: false},
+			expected: string("{\"1\":true,\"2\":false}"),
+		},
+		{
+			name:     "slice",
+			value:    []int{1, 2, 3},
+			expected: string("[1,2,3]"),
 		},
 	}
 	for _, tt := range tests {