diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e8b87a7..7ac9ce1 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,8 +30,8 @@ jobs:
       - name: Check formatting
         run: uv run ruff format --check .
 
-      - name: Run tests
-        run: uv run pytest
+      - name: Run tests with coverage
+        run: uv run pytest --cov=text_toolkit --cov-report=term-missing
 
       - name: Run type checking
         run: uv run mypy
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 7410abc..a57ded4 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -189,7 +189,7 @@ Before opening a pull request with code changes, run the local quality checks:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -205,7 +205,7 @@ Then repeat the checks:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
diff --git a/README.md b/README.md
index 29df75c..ab224ee 100644
--- a/README.md
+++ b/README.md
@@ -121,7 +121,7 @@ Run the same quality checks used by CI:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
diff --git a/docs/06_github_actions.md b/docs/06_github_actions.md
index e472a70..49570f5 100644
--- a/docs/06_github_actions.md
+++ b/docs/06_github_actions.md
@@ -47,7 +47,7 @@ In this project, the local checks are:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -169,6 +169,7 @@ This is important in CI because the workflow should check the project using the
 The `--group dev` option installs development dependencies such as:
 
 - `pytest`,
+- `pytest-cov`,
 - `mypy`,
 - `ruff`.
 
@@ -213,16 +214,18 @@ The developer can fix formatting locally with:
 uv run ruff format .
 ```
 
-## Tests
+## Tests and coverage
 
-The workflow runs tests:
+The workflow runs tests and prints a coverage report:
 
 ```yaml
-- name: Run tests
-  run: uv run pytest
+- name: Run tests with coverage
+  run: uv run pytest --cov=text_toolkit --cov-report=term-missing
 ```
 
-This verifies the behavior of the example package.
+This verifies the behavior of the example package while measuring statement and
+branch coverage. The terminal report shows missing source lines, but the project
+does not fail the workflow based on a coverage percentage.
 
 At this stage, the tests check:
 
diff --git a/docs/07_git_commits_branches_prs.md b/docs/07_git_commits_branches_prs.md
index 0628e5b..dc191a4 100644
--- a/docs/07_git_commits_branches_prs.md
+++ b/docs/07_git_commits_branches_prs.md
@@ -334,7 +334,7 @@ For code changes, run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/08_common_mistakes.md b/docs/08_common_mistakes.md
index fb22e0d..b984a9e 100644
--- a/docs/08_common_mistakes.md
+++ b/docs/08_common_mistakes.md
@@ -145,7 +145,7 @@ For code changes, run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/09_checklist.md b/docs/09_checklist.md
index 0b86639..2fb9ef3 100644
--- a/docs/09_checklist.md
+++ b/docs/09_checklist.md
@@ -140,6 +140,24 @@ uv run mypy
 
 Type checking complements tests and Ruff; it does not replace them.
 
+## Test coverage
+
+The project should use coverage as a diagnostic tool:
+
+- [ ] pytest-cov is installed as a development dependency
+- [ ] coverage is limited to production source code
+- [ ] statement and branch coverage are measured
+- [ ] missing lines are visible in the terminal report
+- [ ] a percentage is not treated as proof of test quality
+
+In this guide, tests and coverage run together:
+
+```bash
+uv run pytest --cov=text_toolkit --cov-report=term-missing
+```
+
+There is no minimum percentage gate.
+
 ## Continuous integration
 
 The project should run checks automatically in CI:
@@ -150,7 +168,7 @@ The project should run checks automatically in CI:
 - [ ] CI installs dependencies from the lockfile
 - [ ] CI runs linting
 - [ ] CI checks formatting
-- [ ] CI runs tests
+- [ ] CI runs tests with coverage reporting
 - [ ] CI runs type checking
 - [ ] CI builds a wheel and source distribution
 - [ ] CI status is visible in the README
@@ -198,7 +216,7 @@ For code changes, run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -214,7 +232,7 @@ Then repeat:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -250,6 +268,7 @@ How do I install it?
 Where is the code?
 Where are the tests?
 How do I run the tests?
+How do I inspect test coverage?
 How do I check formatting and linting?
 How do I check type annotations?
 How do I build distribution files?
diff --git a/docs/12_test_coverage.md b/docs/12_test_coverage.md
index a336a04..434ab1b 100644
--- a/docs/12_test_coverage.md
+++ b/docs/12_test_coverage.md
@@ -97,6 +97,17 @@ The important columns are:
 
 The exact counts will change when the package changes.
 
+## Coverage in CI
+
+The `Quality checks` job runs the same command:
+
+```bash
+uv run pytest --cov=text_toolkit --cov-report=term-missing
+```
+
+The report is visible in the GitHub Actions log. CI fails when tests or coverage
+collection fail, but it does not fail because the percentage decreases.
+
 ## Why there is no percentage gate
 
 This project intentionally does not configure `fail_under`.
diff --git a/docs/ROADMAP.md b/docs/ROADMAP.md
index 341fcac..2421da4 100644
--- a/docs/ROADMAP.md
+++ b/docs/ROADMAP.md
@@ -96,6 +96,7 @@ These parts are already included in the repository.
 - [x] Run linting in CI
 - [x] Run formatting checks in CI
 - [x] Run tests in CI
+- [x] Run coverage reporting in CI
 - [x] Run type checking in CI
 - [x] Build distributions in CI
 - [x] Add a CI badge to the README
@@ -138,10 +139,6 @@ These parts are already included in the repository.
 
 These are good candidates for upcoming small pull requests.
 
-### Test coverage
-
-- [ ] Run coverage reporting in CI and align workflow documentation
-
 ### Repository polish
 
 - [ ] Add issue templates only if the repository starts receiving external feedback
diff --git a/docs/cheatsheet.md b/docs/cheatsheet.md
index 2a22d8d..e0a081e 100644
--- a/docs/cheatsheet.md
+++ b/docs/cheatsheet.md
@@ -62,6 +62,7 @@ Examples:
 uv add --group dev pytest
 uv add --group dev ruff
 uv add --group dev mypy
+uv add --group dev pytest-cov
 ```
 
 Sync the local environment:
@@ -84,6 +85,12 @@ Run tests:
 uv run pytest
 ```
 
+Run tests with coverage:
+
+```bash
+uv run pytest --cov=text_toolkit --cov-report=term-missing
+```
+
 Run type checking:
 
 ```bash
@@ -113,7 +120,7 @@ Run all local checks:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -136,7 +143,7 @@ If formatting fails:
 uv run ruff format .
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -154,7 +161,7 @@ Then run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -250,7 +257,7 @@ uv python install
 uv sync --locked --group dev
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -305,7 +312,7 @@ git status
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/common_questions.md b/docs/common_questions.md
index 3a2a02b..36e4995 100644
--- a/docs/common_questions.md
+++ b/docs/common_questions.md
@@ -224,7 +224,7 @@ This guide first teaches the commands directly:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -305,7 +305,7 @@ Then run the local checks:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/example_pull_request.md b/docs/example_pull_request.md
index 7938ccc..e3c8aa8 100644
--- a/docs/example_pull_request.md
+++ b/docs/example_pull_request.md
@@ -289,7 +289,7 @@ For code changes, run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/from_script_to_project.md b/docs/from_script_to_project.md
index 74fae35..01c0acf 100644
--- a/docs/from_script_to_project.md
+++ b/docs/from_script_to_project.md
@@ -249,6 +249,7 @@ build-backend = "uv_build"
 dev = [
     "mypy>=2.3.1",
     "pytest>=9.0.3",
+    "pytest-cov>=7.1.0",
     "ruff>=0.15.12",
 ]
 
@@ -260,6 +261,13 @@ python_version = "3.12"
 files = ["src", "tests"]
 strict = true
 
+[tool.coverage.run]
+branch = true
+source = ["text_toolkit"]
+
+[tool.coverage.report]
+show_missing = true
+
 [tool.ruff]
 line-length = 88
 target-version = "py312"
@@ -308,7 +316,7 @@ In this guide, the main local checks are:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -317,7 +325,7 @@ These commands check:
 
 - linting,
 - formatting,
-- behavior,
+- behavior and test coverage,
 - type annotations,
 - package distribution builds.
 
@@ -348,7 +356,7 @@ uv python install
 uv sync --locked --group dev
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -429,7 +437,7 @@ The project now has:
 - documentation in `docs/`,
 - dependencies described in `pyproject.toml`,
 - exact dependency versions in `uv.lock`,
-- local checks with Ruff, pytest, and mypy,
+- local checks with Ruff, pytest-cov, and mypy,
 - CI with GitHub Actions,
 - a branch and pull request workflow.
 
diff --git a/docs/github_actions_logs.md b/docs/github_actions_logs.md
index cedd4d3..f0eb565 100644
--- a/docs/github_actions_logs.md
+++ b/docs/github_actions_logs.md
@@ -71,7 +71,7 @@ jobs:
       - name: Install dependencies
       - name: Run Ruff linting
       - name: Check formatting
-      - name: Run tests
+      - name: Run tests with coverage
       - name: Run type checking
       - name: Build distributions
 ```
@@ -288,7 +288,7 @@ After fixing, run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -326,7 +326,7 @@ Then run all checks again:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -339,17 +339,18 @@ git commit -m "style: format files"
 
 If the formatting change is part of another small documentation or code PR, it may be better to amend the existing commit instead of adding a separate formatting-only commit.
 
-## Step: Run tests
+## Step: Run tests with coverage
 
 ### What it does
 
 This step runs:
 
 ```bash
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 ```
 
-It checks whether the code behaves as expected.
+It checks whether the code behaves as expected and reports statement and branch
+coverage for `text_toolkit`. There is no minimum percentage gate.
 
 ### If it fails
 
@@ -364,7 +365,7 @@ Pytest usually shows:
 Example:
 
 ```text
-FAILED tests/test_text_stats.py::test_count_words_handles_repeated_whitespace
+FAILED tests/test_text_stats.py::test_count_characters_includes_whitespace_by_default
 ```
 
 This tells you which test failed.
@@ -382,7 +383,7 @@ assertion error
 Then run tests locally:
 
 ```bash
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 ```
 
 For more detail:
@@ -404,7 +405,7 @@ Then run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -490,7 +491,7 @@ git status
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -620,7 +621,7 @@ Run quality checks:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -723,7 +724,7 @@ A green CI run means:
 - dependencies installed,
 - Ruff linting passed,
 - formatting check passed,
-- tests passed,
+- tests and coverage reporting passed,
 - type checking passed,
 - wheel and source distribution builds passed.
 
diff --git a/docs/glossary.md b/docs/glossary.md
index edec052..25cf4aa 100644
--- a/docs/glossary.md
+++ b/docs/glossary.md
@@ -40,7 +40,7 @@ The CI workflow runs:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
diff --git a/docs/markdown_review.md b/docs/markdown_review.md
index 621ed05..9108564 100644
--- a/docs/markdown_review.md
+++ b/docs/markdown_review.md
@@ -169,7 +169,7 @@ Good:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -382,7 +382,7 @@ However, if the repository has existing quality checks, it is still fine to run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/quickstart_clone_and_ci.md b/docs/quickstart_clone_and_ci.md
index af5ded3..19588cf 100644
--- a/docs/quickstart_clone_and_ci.md
+++ b/docs/quickstart_clone_and_ci.md
@@ -187,10 +187,10 @@ uv sync
 
 ## 6. Run local checks
 
-Run tests:
+Run tests with coverage:
 
 ```bash
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 ```
 
 Run Ruff linting:
@@ -216,7 +216,7 @@ A useful local check sequence is:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -231,7 +231,7 @@ Then repeat:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -241,7 +241,7 @@ If the project is set up correctly:
 
 - Ruff linting should pass,
 - Ruff formatting check should pass,
-- pytest should pass,
+- pytest and coverage reporting should pass,
 - mypy should report no issues.
 
 If one command fails, read the error message before changing anything.
@@ -375,8 +375,8 @@ jobs:
       - name: Check formatting
         run: uv run ruff format --check .
 
-      - name: Run tests
-        run: uv run pytest
+      - name: Run tests with coverage
+        run: uv run pytest --cov=text_toolkit --cov-report=term-missing
 
       - name: Run type checking
         run: uv run mypy
@@ -416,7 +416,7 @@ The CI workflow should run the same checks that developers run locally:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -505,7 +505,7 @@ git status
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -522,7 +522,7 @@ uv sync
 
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -534,7 +534,7 @@ uv python install
 uv sync --locked --group dev
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 uv build --no-sources
 ```
@@ -552,7 +552,7 @@ Before opening a pull request, run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/quickstart_uv.md b/docs/quickstart_uv.md
index 806ea0b..1541c62 100644
--- a/docs/quickstart_uv.md
+++ b/docs/quickstart_uv.md
@@ -107,7 +107,7 @@ def add(left: int, right: int) -> int:
     return left + right
 ```
 
-## 4. Add pytest, Ruff, and mypy as development dependencies
+## 4. Add pytest, pytest-cov, Ruff, and mypy as development dependencies
 
 Add `pytest`:
 
@@ -127,6 +127,12 @@ Add `mypy`:
 uv add --group dev mypy
 ```
 
+Add `pytest-cov`:
+
+```bash
+uv add --group dev pytest-cov
+```
+
 ### Expected result
 
 The project should now contain development dependencies in `pyproject.toml`.
@@ -161,8 +167,8 @@ This adds `rich` to the project dependencies.
 
 The runtime dependency should appear in the `[project]` dependencies section of `pyproject.toml`.
 
-Development tools such as `pytest`, Ruff, and mypy should stay in the
-development dependency group.
+Development tools such as `pytest`, pytest-cov, Ruff, and mypy should stay in
+the development dependency group.
 
 This separation keeps runtime dependencies and development tools easy to understand.
 
@@ -170,7 +176,7 @@ Use runtime dependencies only when the actual package needs them.
 
 Do not add test or linting tools as runtime dependencies.
 
-## 6. Configure pytest, Ruff, and mypy
+## 6. Configure pytest, coverage, Ruff, and mypy
 
 Open `pyproject.toml`.
 
@@ -193,6 +199,7 @@ build-backend = "uv_build"
 dev = [
     "mypy>=2.3.1",
     "pytest>=9.0.3",
+    "pytest-cov>=7.1.0",
     "ruff>=0.15.12",
 ]
 
@@ -204,6 +211,13 @@ python_version = "3.12"
 files = ["src", "tests"]
 strict = true
 
+[tool.coverage.run]
+branch = true
+source = ["example_project"]
+
+[tool.coverage.report]
+show_missing = true
+
 [tool.ruff]
 line-length = 88
 target-version = "py312"
@@ -291,10 +305,10 @@ Do not commit `.venv/` to Git.
 
 ## 9. Run commands inside the environment
 
-Run tests:
+Run tests with coverage:
 
 ```bash
-uv run pytest
+uv run pytest --cov=example_project --cov-report=term-missing
 ```
 
 Run Ruff linting:
@@ -325,7 +339,7 @@ uv run ruff format .
 
 If everything is configured correctly:
 
-- `uv run pytest` should pass,
+- `uv run pytest --cov=example_project --cov-report=term-missing` should pass,
 - `uv run ruff check .` should pass,
 - `uv run ruff format --check .` should pass,
 - `uv run mypy` should report no issues.
@@ -367,7 +381,7 @@ For everyday development, use:
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=example_project --cov-report=term-missing
 uv run mypy
 ```
 
@@ -377,7 +391,7 @@ If formatting fails:
 uv run ruff format .
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=example_project --cov-report=term-missing
 uv run mypy
 ```
 
@@ -420,13 +434,14 @@ touch tests/test_calculator.py
 uv add --group dev pytest
 uv add --group dev ruff
 uv add --group dev mypy
+uv add --group dev pytest-cov
 uv add rich
 
 uv sync
 
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=example_project --cov-report=term-missing
 uv run mypy
 ```
 
diff --git a/docs/troubleshooting.md b/docs/troubleshooting.md
index 38fe071..9f9d7e5 100644
--- a/docs/troubleshooting.md
+++ b/docs/troubleshooting.md
@@ -14,7 +14,7 @@ uv --version
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -261,7 +261,7 @@ Then check again:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -302,7 +302,7 @@ Then run all checks again:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -388,10 +388,40 @@ Then run:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
+## Coverage reporting fails
+
+### Problem
+
+Tests may pass without coverage, but this command fails:
+
+```bash
+uv run pytest --cov=text_toolkit --cov-report=term-missing
+```
+
+### Possible causes
+
+- pytest-cov is missing from the development dependency group,
+- the local environment is out of sync,
+- the package name passed to `--cov` is incorrect,
+- coverage configuration is invalid.
+
+### Fix
+
+Sync dependencies and retry:
+
+```bash
+uv sync
+uv run pytest --cov=text_toolkit --cov-report=term-missing
+```
+
+Check that `pyproject.toml` contains pytest-cov and the `[tool.coverage.run]`
+section. A lower percentage by itself does not fail this project because no
+`fail_under` threshold is configured.
+
 ## `uv.lock` is out of sync
 
 ### Problem
@@ -436,7 +466,7 @@ Run checks again:
 ```bash
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -627,7 +657,7 @@ git status
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -665,7 +695,7 @@ Run:
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```
 
@@ -765,7 +795,7 @@ git status
 uv sync
 uv run ruff check .
 uv run ruff format --check .
-uv run pytest
+uv run pytest --cov=text_toolkit --cov-report=term-missing
 uv run mypy
 ```