Add better hints for string type mismatch

go.mod

@@ -6,6 +6,7 @@ toolchain go1.24.2
 
 require (
 	github.com/codecrafters-io/tester-utils v0.4.9
+	github.com/dustin/go-humanize v1.0.1
 	github.com/hdt3213/rdb v1.2.0
 	github.com/stretchr/testify v1.10.0
 	github.com/tidwall/pretty v1.2.1
@@ -14,7 +15,6 @@ require (
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/fatih/color v1.18.0 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect

internal/resp_assertions/bulk_string_assertion.go

@@ -15,6 +15,15 @@ func NewBulkStringAssertion(expectedValue string) RESPAssertion {
 }
 
 func (a BulkStringAssertion) Run(value resp_value.Value) error {
+	// Frequently occurs in user submissions
+	if value.Type == resp_value.SIMPLE_STRING && value.String() == a.ExpectedValue {
+		return fmt.Errorf(
+			"Expected bulk string \"%s\", got simple string \"%s\" instead",
+			a.ExpectedValue,
+			value.String(),
+		)
+	}
+
 	bulkStringTypeAssertion := DataTypeAssertion{ExpectedType: resp_value.BULK_STRING}
 
 	if err := bulkStringTypeAssertion.Run(value); err != nil {

internal/resp_assertions/bulk_string_present_in_array_assertion.go

@@ -25,5 +25,16 @@ func (a BulkStringPresentInArrayAssertion) Run(value resp_value.Value) error {
 		}
 	}
 
+	// Possible frequent-occurence inferring from the existing errors in user submissions
+	for _, element := range array {
+		if element.Type == resp_value.SIMPLE_STRING && element.String() == a.ExpectedString {
+			return fmt.Errorf(
+				"Expected bulk string '%s' to be present in the array, but simple string '%s' is present instead",
+				a.ExpectedString,
+				element.String(),
+			)
+		}
+	}
+
 	return fmt.Errorf("Expected bulk string '%s' to be present in the array, but is absent", a.ExpectedString)
 }

internal/resp_assertions/simple_string_assertion.go

@@ -15,6 +15,15 @@ func NewSimpleStringAssertion(expectedValue string) RESPAssertion {
 }
 
 func (a SimpleStringAssertion) Run(value resp_value.Value) error {
+	// Frequently occurs in user submissions
+	if value.Type == resp_value.BULK_STRING && value.String() == a.ExpectedValue {
+		return fmt.Errorf(
+			"Expected simple string \"%s\", got bulk string \"%s\" instead",
+			a.ExpectedValue,
+			value.String(),
+		)
+	}
+
 	simpleStringTypeAssertion := DataTypeAssertion{ExpectedType: resp_value.SIMPLE_STRING}
 
 	if err := simpleStringTypeAssertion.Run(value); err != nil {

internal/stages_test.go

@@ -61,6 +61,13 @@ func TestStages(t *testing.T) {
 			StdoutFixturePath:   "./test_helpers/fixtures/ping-pong/without_read_multiple_pongs",
 			NormalizeOutputFunc: normalizeTesterOutput,
 		},
+		"ping_pong_string_type_mismatch": {
+			StageSlugs:          []string{"rg2"},
+			CodePath:            "./test_helpers/scenarios/ping-pong/string_type_mismatch",
+			ExpectedExitCode:    1,
+			StdoutFixturePath:   "./test_helpers/fixtures/ping-pong/string_type_mismatch",
+			NormalizeOutputFunc: normalizeTesterOutput,
+		},
 		"invalid_resp_error": {
 			StageSlugs:          []string{"rg2"},
 			CodePath:            "./test_helpers/scenarios/invalid-resp/",

internal/test_helpers/fixtures/ping-pong/string_type_mismatch

@@ -0,0 +1,14 @@
+Debug = true
+
+[tester::#RG2] Running tests for Stage #RG2 (rg2)
+[tester::#RG2] $ ./spawn_redis_server.sh
+[your_program] hey, binding to 6379
+[tester::#RG2] Connection established, sending ping command...
+[tester::#RG2] [client] $ redis-cli PING
+[tester::#RG2] [client] Sent bytes: "*1\r\n$4\r\nPING\r\n"
+[tester::#RG2] [client] Received bytes: "$4\r\nPONG\r\n"
+[tester::#RG2] [client] Received RESP bulk string: "PONG"
+[tester::#RG2] Expected simple string "PONG", got bulk string "PONG" instead
+[tester::#RG2] Test failed
+[tester::#RG2] Terminating program
+[tester::#RG2] Program terminated successfully

internal/test_helpers/scenarios/ping-pong/string_type_mismatch/codecrafters.yml

@@ -0,0 +1,5 @@
+# Set this to true if you want debug logs.
+#
+# These can be VERY verbose, so we suggest turning them off
+# unless you really need them.
+debug: true

internal/test_helpers/scenarios/ping-pong/string_type_mismatch/spawn_redis_server.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env -S python3 -u
+import socket
+import time
+print("hey, binding to 6379")
+sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+
+sock.bind(('', 6379))
+
+sock.listen(1)
+
+conn, cli_addr = sock.accept()
+
+# Send bulk string instead of simple string
+conn.send(b"$4\r\nPONG\r\n")