diff --git a/.claude/rules/testing.md b/.claude/rules/testing.md
index b9c617b5..03ba6e4c 100644
--- a/.claude/rules/testing.md
+++ b/.claude/rules/testing.md
@@ -33,7 +33,14 @@ assert_file_not_exists "$path"
 assert_directory_exists "$path"
 assert_array_contains "value" "${array[@]}"
 assert_array_not_contains "value" "${array[@]}"
-assert_fails "assert_equals 'a' 'b'"
+```
+
+There is no `assert_fails`. To assert that an assertion *fails*, capture its output and
+compare it with the renderer:
+
+```bash
+assert_same "$(bashunit::console_results::print_failed_test "My test" "a" "but got " "b")" \
+  "$(assert_same "a" "b")"
 ```
 
 ## Test Doubles
diff --git a/.claude/skills/add-assertion/SKILL.md b/.claude/skills/add-assertion/SKILL.md
index 4bf4355d..810a9bf4 100644
--- a/.claude/skills/add-assertion/SKILL.md
+++ b/.claude/skills/add-assertion/SKILL.md
@@ -33,7 +33,8 @@ Read `src/assertions.sh` and `tests/unit/assert_test.sh` to understand:
 For each test in inventory, follow RED -> GREEN -> REFACTOR:
 
 1. **Basic success case** — assertion passes with valid input
-2. **Failure case** — assertion fails correctly, use `assert_fails`
+2. **Failure case** — assertion fails correctly: capture its output and compare it with
+   `bashunit::console_results::print_failed_test` (there is no `assert_fails`)
 3. **Edge cases** — empty input, special characters, nested structures, malformed data
 
 ### 4. Integration
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9ae0196a..93526da9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@
 - The `--parallel` unsupported-OS warning no longer claims Alpine is excluded
 
 ### Fixed
+- Call assertions (`assert_not_called`, `assert_have_been_called*`) fail with `was never registered as a spy` instead of reporting zero calls when the name was never spied — a typo used to pass silently (#895)
 - The per-argument form a spy records was written with a literal `$'\x1f'` separator instead of the byte, so it could not be compared against (#894)
 - `--parallel` no longer discards worker stderr written outside a test body; it renders as a `Stderr from <file>` block (#864)
 - The minimum-bash gate compares the minor version and parses suffixed versions; the floor is unchanged at **Bash 3.0+**
diff --git a/docs/ai-agents.md b/docs/ai-agents.md
index 1567d19b..04941214 100644
--- a/docs/ai-agents.md
+++ b/docs/ai-agents.md
@@ -114,6 +114,9 @@ actually make against this API:
 - Spy assertion argument order is inconsistent — check, don't guess:
   `assert_have_been_called_times <count> <spy>` but
   `assert_have_been_called_with <spy> <expected> [call_index]`.
+- A call assertion on a name that was never passed to `bashunit::spy` fails with
+  `was never registered as a spy`. Spies do not survive across tests, so register the
+  spy inside the test that asserts on it.
 - `assert_have_been_called_with` joins the expected arguments with spaces, so it cannot
   tell `cmd "a b"` from `cmd a b` — a quoting bug passes it. Use
   `assert_have_been_called_with_args <spy> <arg>...` (no `call_index`) to compare
diff --git a/docs/public/bashunit-skill.md b/docs/public/bashunit-skill.md
index bce8ab90..b7879174 100644
--- a/docs/public/bashunit-skill.md
+++ b/docs/public/bashunit-skill.md
@@ -165,6 +165,10 @@ failing_command || ec=$?            # correct
 local out; out=$(failing_command)   # WRONG under set -e
 ```
 
+**Spies do not survive across tests, and a call assertion on an unregistered name fails**
+with `was never registered as a spy` (it used to report zero calls, so `assert_not_called`
+with a typo passed while asserting nothing). Register the spy in the test that asserts on it.
+
 **`assert_have_been_called_with` joins arguments with spaces**, so it cannot see argument
 boundaries: `touch "a b"` also satisfies `assert_have_been_called_with touch "a" "b"`. When
 an argument may contain a space — any path — use `assert_have_been_called_with_args`, which
diff --git a/docs/test-doubles.md b/docs/test-doubles.md
index 98bfae25..fbf1be6f 100644
--- a/docs/test-doubles.md
+++ b/docs/test-doubles.md
@@ -127,6 +127,18 @@ function test_example() {
 ```
 :::
 
+::: tip Call assertions require a registered spy
+Every `assert_have_been_called*` / `assert_not_called` assertion fails when the name it targets was never passed to `bashunit::spy` — or was removed by `bashunit::unmock`, or belongs to a previous test:
+
+```
+✗ Failed: My test
+    Expected 'tuoch'
+    was never registered as a spy; call it first with 'bashunit::spy tuoch'
+```
+
+Without that check a typo would report zero calls, so `assert_not_called tuoch` would pass while asserting nothing. Spies are cleared between tests, so spy inside the test that asserts on them.
+:::
+
 ## assert_have_been_called
 > `assert_have_been_called "spy"`
 
diff --git a/src/test_doubles.sh b/src/test_doubles.sh
index 0cf23d5e..e73ddc88 100644
--- a/src/test_doubles.sh
+++ b/src/test_doubles.sh
@@ -8,21 +8,37 @@ declare -a _BASHUNIT_MOCKED_FUNCTIONS=()
 # resolves `_BASHUNIT_SPY_foo_TIMES_FILE` instead.
 
 _BASHUNIT_SPY_TIMES_OUT=0
+_BASHUNIT_SPY_REGISTERED_OUT=false
 
 # Reads the recorded call count for $1 into _BASHUNIT_SPY_TIMES_OUT (0 when
-# never spied/called). Shared by the call-count assertions instead of each
-# repeating the "resolve times file, cat it, default to 0" sequence.
+# never called) and whether $1 is a live spy into _BASHUNIT_SPY_REGISTERED_OUT.
+# Shared by the call-count assertions instead of each repeating the "resolve
+# times file, cat it, default to 0" sequence.
 function bashunit::spy::times_to_slot() {
   local command="$1"
   local variable
   variable="$(bashunit::helper::normalize_variable_name "$command")"
   local file_var="_BASHUNIT_SPY_${variable}_TIMES_FILE"
   _BASHUNIT_SPY_TIMES_OUT=0
+  _BASHUNIT_SPY_REGISTERED_OUT=false
+  if [ -n "${!file_var-}" ]; then
+    _BASHUNIT_SPY_REGISTERED_OUT=true
+  fi
   if [ -f "${!file_var-}" ]; then
     _BASHUNIT_SPY_TIMES_OUT=$(cat "${!file_var}" 2>/dev/null || builtin echo 0)
   fi
 }
 
+# Fails the calling assertion because $1 is not a registered spy. Reporting
+# "never called" for a name that was never spied — a typo, or a spy that was
+# unmocked — makes the assertion vacuous while still printing green.
+# Arguments: $1 - command, $2 - test label
+function bashunit::spy::fail_unregistered() {
+  bashunit::state::add_assertions_failed
+  bashunit::console_results::print_failed_test "$2" "$1" \
+    "was never registered as a spy; call it first with" "bashunit::spy $1"
+}
+
 _BASHUNIT_SPY_SERIALIZED_OUT=""
 
 # Serializes the given arguments into _BASHUNIT_SPY_SERIALIZED_OUT exactly the
@@ -137,6 +153,11 @@ function assert_have_been_called() {
   local times=$_BASHUNIT_SPY_TIMES_OUT
   local label="${2:-$(bashunit::helper::normalize_test_function_name "${FUNCNAME[1]}")}"
 
+  if [ "$_BASHUNIT_SPY_REGISTERED_OUT" = false ]; then
+    bashunit::spy::fail_unregistered "$command" "$label"
+    return
+  fi
+
   if [ "$times" -eq 0 ]; then
     bashunit::state::add_assertions_failed
     bashunit::console_results::print_failed_test "${label}" "${command}" "to have been called" "once"
@@ -166,6 +187,14 @@ function assert_have_been_called_with() {
   local variable
   variable="$(bashunit::helper::normalize_variable_name "$command")"
   local file_var="_BASHUNIT_SPY_${variable}_PARAMS_FILE"
+  local label
+  label="$(bashunit::helper::normalize_test_function_name "${FUNCNAME[1]}")"
+
+  if [ -z "${!file_var-}" ]; then
+    bashunit::spy::fail_unregistered "$command" "$label"
+    return
+  fi
+
   local line=""
   if [ -f "${!file_var-}" ]; then
     if [ -n "$index" ]; then
@@ -180,8 +209,7 @@ function assert_have_been_called_with() {
 
   if [ "$expected" != "$raw" ]; then
     bashunit::state::add_assertions_failed
-    bashunit::console_results::print_failed_test "$(bashunit::helper::normalize_test_function_name \
-      "${FUNCNAME[1]}")" "$expected" "but got " "$raw"
+    bashunit::console_results::print_failed_test "$label" "$expected" "but got " "$raw"
     return
   fi
 
@@ -198,6 +226,14 @@ function assert_have_been_called_with_args() {
   local variable
   variable="$(bashunit::helper::normalize_variable_name "$command")"
   local file_var="_BASHUNIT_SPY_${variable}_PARAMS_FILE"
+  local label
+  label="$(bashunit::helper::normalize_test_function_name "${FUNCNAME[1]}")"
+
+  if [ -z "${!file_var-}" ]; then
+    bashunit::spy::fail_unregistered "$command" "$label"
+    return
+  fi
+
   local line=""
   if [ -f "${!file_var-}" ]; then
     line=$(tail -n 1 "${!file_var}" 2>/dev/null || true)
@@ -208,8 +244,8 @@ function assert_have_been_called_with_args() {
 
   if [ "$expected" != "$actual" ]; then
     bashunit::state::add_assertions_failed
-    bashunit::console_results::print_failed_test "$(bashunit::helper::normalize_test_function_name \
-      "${FUNCNAME[1]}")" "${expected//$'\x1f'/ }" "but got " "${actual//$'\x1f'/ }"
+    bashunit::console_results::print_failed_test "$label" \
+      "${expected//$'\x1f'/ }" "but got " "${actual//$'\x1f'/ }"
     return
   fi
 
@@ -222,6 +258,12 @@ function assert_have_been_called_times() {
   bashunit::spy::times_to_slot "$command"
   local times=$_BASHUNIT_SPY_TIMES_OUT
   local label="${3:-$(bashunit::helper::normalize_test_function_name "${FUNCNAME[1]}")}"
+
+  if [ "$_BASHUNIT_SPY_REGISTERED_OUT" = false ]; then
+    bashunit::spy::fail_unregistered "$command" "$label"
+    return
+  fi
+
   if [ "$times" -ne "$expected_count" ]; then
     bashunit::state::add_assertions_failed
     bashunit::console_results::print_failed_test "${label}" "${command}" \
@@ -248,6 +290,11 @@ function assert_have_been_called_nth_with() {
   bashunit::spy::times_to_slot "$command"
   local times=$_BASHUNIT_SPY_TIMES_OUT
 
+  if [ "$_BASHUNIT_SPY_REGISTERED_OUT" = false ]; then
+    bashunit::spy::fail_unregistered "$command" "$label"
+    return
+  fi
+
   if [ "$nth" -gt "$times" ]; then
     bashunit::state::add_assertions_failed
     bashunit::console_results::print_failed_test "${label}" \
diff --git a/tests/acceptance/mock_test.sh b/tests/acceptance/mock_test.sh
index 40a483a9..8a07c507 100644
--- a/tests/acceptance/mock_test.sh
+++ b/tests/acceptance/mock_test.sh
@@ -16,5 +16,10 @@ function test_runner_clear_mocks_first() {
 
 function test_runner_clear_mocks_second() {
   assert_not_equals "foo" "$(ls)"
-  assert_have_been_called_times 0 ps
+  # The spy registered by the first test is gone, so a call assertion on `ps`
+  # now reports an unregistered spy rather than zero calls.
+  assert_same \
+    "$(bashunit::console_results::print_failed_test "Runner clear mocks second" "ps" \
+      "was never registered as a spy; call it first with" "bashunit::spy ps")" \
+    "$(assert_have_been_called_times 0 ps)"
 }
diff --git a/tests/functional/doubles_test.sh b/tests/functional/doubles_test.sh
index 4ba6b86a..f4128314 100644
--- a/tests/functional/doubles_test.sh
+++ b/tests/functional/doubles_test.sh
@@ -127,6 +127,48 @@ function test_spy_call_with_args_detects_wrong_argument_boundaries() {
     "$(assert_have_been_called_with_args spy_boundary_command "a" "b")"
 }
 
+function test_assert_not_called_fails_when_the_command_was_never_spied() {
+  assert_same \
+    "$(bashunit::console_results::print_failed_test \
+      "Assert not called fails when the command was never spied" \
+      "never_spied_command" "was never registered as a spy; call it first with" \
+      "bashunit::spy never_spied_command")" \
+    "$(assert_not_called never_spied_command)"
+}
+
+function test_call_assertions_fail_when_the_command_was_never_spied() {
+  local label="Call assertions fail when the command was never spied"
+  local expected
+  expected="$(bashunit::console_results::print_failed_test "$label" \
+    "never_spied_command" "was never registered as a spy; call it first with" \
+    "bashunit::spy never_spied_command")"
+
+  assert_same "$expected" "$(assert_have_been_called never_spied_command)"
+  assert_same "$expected" "$(assert_have_been_called_times 0 never_spied_command)"
+  assert_same "$expected" "$(assert_have_been_called_with never_spied_command "x")"
+  assert_same "$expected" "$(assert_have_been_called_with_args never_spied_command "x")"
+  assert_same "$expected" "$(assert_have_been_called_nth_with 1 never_spied_command "x")"
+}
+
+function test_call_assertions_fail_after_the_spy_was_unmocked() {
+  bashunit::spy spy_to_be_unmocked
+  bashunit::unmock spy_to_be_unmocked
+
+  assert_same \
+    "$(bashunit::console_results::print_failed_test \
+      "Call assertions fail after the spy was unmocked" \
+      "spy_to_be_unmocked" "was never registered as a spy; call it first with" \
+      "bashunit::spy spy_to_be_unmocked")" \
+    "$(assert_not_called spy_to_be_unmocked)"
+}
+
+function test_assert_not_called_still_passes_on_a_registered_spy() {
+  bashunit::spy spy_never_invoked
+
+  assert_empty "$(assert_not_called spy_never_invoked)"
+  assert_empty "$(assert_have_been_called_times 0 spy_never_invoked)"
+}
+
 function test_spy_on_echo_does_not_hang() {
   source ./tests/functional/fixtures/echo_function.sh
   bashunit::spy echo