diff --git a/lib/elixir_analyzer/constants.ex b/lib/elixir_analyzer/constants.ex
index 19247b35..5496a545 100644
--- a/lib/elixir_analyzer/constants.ex
+++ b/lib/elixir_analyzer/constants.ex
@@ -76,7 +76,7 @@ defmodule ElixirAnalyzer.Constants do
     captains_log_do_not_use_enum_random: "elixir.captains-log.do_not_use_enum_random",
     captains_log_do_not_use_rand_uniform_real: "elixir.captains-log.do_not_use_rand_uniform_real",
     captains_log_use_rand_uniform: "elixir.captains-log.use_rand_uniform",
-    captains_log_use_io_lib: "elixir.captains-log.use_io_lib",
+    captains_log_use_erlang: "elixir.captains-log.use_erlang",
 
     # Community Garden Comments
     community_garden_use_get_and_update: "elixir.community-garden.use_get_and_update",
diff --git a/lib/elixir_analyzer/test_suite/captains_log.ex b/lib/elixir_analyzer/test_suite/captains_log.ex
index 05a1256e..e21b6d91 100644
--- a/lib/elixir_analyzer/test_suite/captains_log.ex
+++ b/lib/elixir_analyzer/test_suite/captains_log.ex
@@ -4,6 +4,7 @@ defmodule ElixirAnalyzer.TestSuite.CaptainsLog do
   """
   use ElixirAnalyzer.ExerciseTest
   alias ElixirAnalyzer.Constants
+  alias ElixirAnalyzer.Source
 
   assert_call "random_planet_class uses Enum.random" do
     type :essential
@@ -43,10 +44,30 @@ defmodule ElixirAnalyzer.TestSuite.CaptainsLog do
     suppress_if "random_stardate does not use Enum.random", :fail
   end
 
-  assert_call "format_stardate uses :io_lib" do
+
+  check_source "format_stardate uses erlang" do
     type :essential
-    calling_fn module: CaptainsLog, name: :format_stardate
-    called_fn module: :io_lib, name: :_
-    comment Constants.captains_log_use_io_lib()
+    comment Constants.captains_log_use_erlang()
+
+    check(%Source{code_ast: code_ast}) do
+      {_, erlang?} =
+        Macro.prewalk(code_ast, false, fn node, acc ->
+          case node do
+            # usage :io_lib.format/2
+            {{:., _, [:io_lib, :format]}, _, _} ->
+              {node, true}
+
+            # usage :erlang.function_name/arity
+            # matches any function call from :erlang module
+            {{:., _, [:erlang, _]}, _, _} ->
+              {node, true}
+
+            _ ->
+              {node, acc}
+          end
+        end)
+
+      erlang?
+    end
   end
 end
diff --git a/test/elixir_analyzer/test_suite/captains_log_test.exs b/test/elixir_analyzer/test_suite/captains_log_test.exs
index b3b783fd..fb07b638 100644
--- a/test/elixir_analyzer/test_suite/captains_log_test.exs
+++ b/test/elixir_analyzer/test_suite/captains_log_test.exs
@@ -98,7 +98,7 @@ defmodule ElixirAnalyzer.ExerciseTest.CaptainsLogTest do
   end
 
   test_exercise_analysis "format_stardate uses Float.round",
-    comments_include: [Constants.captains_log_use_io_lib()] do
+    comments_include: [Constants.captains_log_use_erlang()] do
     defmodule CaptainsLog do
       def format_stardate(stardate) do
         if is_float(stardate) do
diff --git a/test_data/captains-log/no_erlang_solution/.meta/config.json b/test_data/captains-log/no_erlang_solution/.meta/config.json
new file mode 100644
index 00000000..d279010d
--- /dev/null
+++ b/test_data/captains-log/no_erlang_solution/.meta/config.json
@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "angelikatyborska"
+  ],
+  "contributors": [
+    "neenjaw"
+  ],
+  "files": {
+    "solution": [
+      "lib/captains_log.ex"
+    ],
+    "test": [
+      "test/captains_log_test.exs"
+    ],
+    "exemplar": [
+      ".meta/exemplar.ex"
+    ]
+  },
+  "blurb": "Learn about randomness and using Erlang libraries from Elixir by helping Mary generate stardates and starship registry numbers for her Star Trek themed pen-and-paper role playing sessions."
+}
\ No newline at end of file
diff --git a/test_data/captains-log/no_erlang_solution/.meta/exemplar.ex b/test_data/captains-log/no_erlang_solution/.meta/exemplar.ex
new file mode 100644
index 00000000..faaff587
--- /dev/null
+++ b/test_data/captains-log/no_erlang_solution/.meta/exemplar.ex
@@ -0,0 +1,20 @@
+defmodule CaptainsLog do
+  @planetary_classes ["D", "H", "J", "K", "L", "M", "N", "R", "T", "Y"]
+
+  def random_planet_class() do
+    Enum.random(@planetary_classes)
+  end
+
+  def random_ship_registry_number() do
+    number = Enum.random(1000..9999)
+    "NCC-#{number}"
+  end
+
+  def random_stardate() do
+    :rand.uniform() * 1000 + 41_000
+  end
+
+  def format_stardate(stardate) do
+    to_string(:io_lib.format("~.1f", [stardate]))
+  end
+end
diff --git a/test_data/captains-log/no_erlang_solution/expected_analysis.json b/test_data/captains-log/no_erlang_solution/expected_analysis.json
new file mode 100644
index 00000000..b8b95c54
--- /dev/null
+++ b/test_data/captains-log/no_erlang_solution/expected_analysis.json
@@ -0,0 +1 @@
+{"summary":"Check the comments for things to fix. 🛠","comments":[{"type":"essential","comment":"elixir.captains-log.use_erlang"},{"type":"informative","params":{"mentoring_request_url":"https://exercism.org/tracks/elixir/exercises/captains-log/mentor_discussions"},"comment":"elixir.general.feedback_request"}]}
\ No newline at end of file
diff --git a/test_data/captains-log/no_erlang_solution/lib/captains_log.ex b/test_data/captains-log/no_erlang_solution/lib/captains_log.ex
new file mode 100644
index 00000000..4666af3a
--- /dev/null
+++ b/test_data/captains-log/no_erlang_solution/lib/captains_log.ex
@@ -0,0 +1,20 @@
+defmodule CaptainsLog do
+  @planetary_classes ["D", "H", "J", "K", "L", "M", "N", "R", "T", "Y"]
+
+  def random_planet_class() do
+    Enum.random(@planetary_classes)
+  end
+
+  def random_ship_registry_number() do
+    number = Enum.random(1000..9999)
+    "NCC-#{number}"
+  end
+
+  def random_stardate() do
+    :rand.uniform() * 1000 + 41_000
+  end
+
+  def format_stardate(stardate) do
+    Float.round(stardate, 1) |> to_string()
+  end
+end
diff --git a/test_data/captains-log/perfect_solution/.meta/config.json b/test_data/captains-log/perfect_solution/.meta/config.json
new file mode 100644
index 00000000..d279010d
--- /dev/null
+++ b/test_data/captains-log/perfect_solution/.meta/config.json
@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "angelikatyborska"
+  ],
+  "contributors": [
+    "neenjaw"
+  ],
+  "files": {
+    "solution": [
+      "lib/captains_log.ex"
+    ],
+    "test": [
+      "test/captains_log_test.exs"
+    ],
+    "exemplar": [
+      ".meta/exemplar.ex"
+    ]
+  },
+  "blurb": "Learn about randomness and using Erlang libraries from Elixir by helping Mary generate stardates and starship registry numbers for her Star Trek themed pen-and-paper role playing sessions."
+}
\ No newline at end of file
diff --git a/test_data/captains-log/perfect_solution/.meta/exemplar.ex b/test_data/captains-log/perfect_solution/.meta/exemplar.ex
new file mode 100644
index 00000000..faaff587
--- /dev/null
+++ b/test_data/captains-log/perfect_solution/.meta/exemplar.ex
@@ -0,0 +1,20 @@
+defmodule CaptainsLog do
+  @planetary_classes ["D", "H", "J", "K", "L", "M", "N", "R", "T", "Y"]
+
+  def random_planet_class() do
+    Enum.random(@planetary_classes)
+  end
+
+  def random_ship_registry_number() do
+    number = Enum.random(1000..9999)
+    "NCC-#{number}"
+  end
+
+  def random_stardate() do
+    :rand.uniform() * 1000 + 41_000
+  end
+
+  def format_stardate(stardate) do
+    to_string(:io_lib.format("~.1f", [stardate]))
+  end
+end
diff --git a/test_data/captains-log/perfect_solution/expected_analysis.json b/test_data/captains-log/perfect_solution/expected_analysis.json
new file mode 100644
index 00000000..9dfbf803
--- /dev/null
+++ b/test_data/captains-log/perfect_solution/expected_analysis.json
@@ -0,0 +1 @@
+{"comments":[],"summary":"Submission analyzed. No automated suggestions found."}
diff --git a/test_data/captains-log/perfect_solution/lib/captains_log.ex b/test_data/captains-log/perfect_solution/lib/captains_log.ex
new file mode 100644
index 00000000..86678ca8
--- /dev/null
+++ b/test_data/captains-log/perfect_solution/lib/captains_log.ex
@@ -0,0 +1,20 @@
+defmodule CaptainsLog do
+  @planetary_classes ["D", "H", "J", "K", "L", "M", "N", "R", "T", "Y"]
+
+  def random_planet_class() do
+    Enum.random(@planetary_classes)
+  end
+
+  def random_ship_registry_number() do
+    number = Enum.random(1000..9999)
+    "NCC-#{number}"
+  end
+
+  def random_stardate() do
+    :rand.uniform() * 1000 + 41_000
+  end
+
+  def format_stardate(stardate) do
+    :io_lib.format("~.1f", [stardate]) |> to_string()
+  end
+end