diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b2034b0..1477917 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,3 +36,30 @@ jobs:
             grep -E '^test result:|^running' test-output.txt >> "$GITHUB_STEP_SUMMARY" || true
             echo '```' >> "$GITHUB_STEP_SUMMARY"
           fi
+
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: llvm-tools-preview
+      - uses: Swatinem/rust-cache@v2
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
+      - name: Generate coverage report
+        run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
+      - name: Upload to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          files: lcov.info
+          fail_ci_if_error: true
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+      - name: Job summary
+        if: always()
+        run: |
+          echo "## Coverage" >> "$GITHUB_STEP_SUMMARY"
+          echo '```' >> "$GITHUB_STEP_SUMMARY"
+          cargo llvm-cov report --summary-only 2>/dev/null >> "$GITHUB_STEP_SUMMARY" || true
+          echo '```' >> "$GITHUB_STEP_SUMMARY"
diff --git a/.gitignore b/.gitignore
index 96ef6c0..32a86fc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 /target
 Cargo.lock
+lcov.info
diff --git a/Makefile b/Makefile
index 479dcff..55f62ea 100644
--- a/Makefile
+++ b/Makefile
@@ -1,13 +1,17 @@
-.PHONY: help check test fmt lint doc ci
+.PHONY: help check test fmt lint doc ci cov cov-report cov-regions install-dev
 
 help:
 	@echo "Available targets:"
-	@echo "  check   Check workspace compiles"
-	@echo "  test    Run all tests"
-	@echo "  fmt     Format code"
-	@echo "  lint    Run clippy with warnings as errors"
-	@echo "  doc     Build and open docs in browser"
-	@echo "  ci      Run all CI checks locally (fmt, clippy, test, doc)"
+	@echo "  check        Check workspace compiles"
+	@echo "  test         Run all tests"
+	@echo "  fmt          Format code"
+	@echo "  lint         Run clippy with warnings as errors"
+	@echo "  doc          Build and open docs in browser"
+	@echo "  cov          Generate HTML coverage report and open it"
+	@echo "  cov-report   Print uncovered lines"
+	@echo "  cov-regions  Print uncovered regions with context"
+	@echo "  ci           Run all CI checks locally (fmt, clippy, test, doc)"
+	@echo "  install-dev  Install local dev tools (cargo-llvm-cov)"
 
 # Check workspace compiles
 check:
@@ -29,6 +33,23 @@ lint:
 doc:
 	cargo doc --no-deps -p wavekat-core --all-features --open
 
+# Install local dev tools (run once after cloning)
+install-dev:
+	rustup component add llvm-tools-preview
+	cargo install cargo-llvm-cov
+
+# Generate HTML coverage report and open it in the browser
+cov:
+	cargo llvm-cov --all-features --open
+
+# Print uncovered lines only (paste into Claude Code to write tests)
+cov-report:
+	@cargo llvm-cov --all-features --text 2>/dev/null | grep -E '\|[[:space:]]+0\|' || echo "No uncovered lines."
+
+# Print uncovered regions with source context (paste into Claude Code to write tests)
+cov-regions:
+	@cargo llvm-cov --all-features --text 2>/dev/null | grep -B1 '\^0' || echo "No uncovered regions."
+
 # Run all CI checks locally (mirrors .github/workflows/ci.yml)
 ci:
 	cargo fmt --all -- --check
diff --git a/README.md b/README.md
index f0d881b..3251d56 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,7 @@
 
 [![Crates.io](https://img.shields.io/crates/v/wavekat-core.svg)](https://crates.io/crates/wavekat-core)
 [![docs.rs](https://docs.rs/wavekat-core/badge.svg)](https://docs.rs/wavekat-core)
+[![codecov](https://codecov.io/gh/wavekat/wavekat-core/branch/main/graph/badge.svg)](https://codecov.io/gh/wavekat/wavekat-core)
 
 Shared types for the WaveKat audio processing ecosystem.
 
diff --git a/codecov.yml b/codecov.yml
new file mode 100644
index 0000000..6e99a73
--- /dev/null
+++ b/codecov.yml
@@ -0,0 +1,13 @@
+coverage:
+  status:
+    project:
+      default:
+        target: auto   # must not drop below current coverage
+        threshold: 1%  # allow up to 1% drop before failing
+    patch:
+      default:
+        target: 80%    # new code in PRs must be at least 80% covered
+
+comment:
+  layout: "reach,diff,flags,tree"
+  behavior: default    # post once, update on new commits
diff --git a/crates/wavekat-core/src/audio.rs b/crates/wavekat-core/src/audio.rs
index 2b180b7..d521573 100644
--- a/crates/wavekat-core/src/audio.rs
+++ b/crates/wavekat-core/src/audio.rs
@@ -311,4 +311,42 @@ mod tests {
         assert_eq!(frame.samples().as_ptr(), ptr);
         assert_eq!(frame.sample_rate(), 24000);
     }
+
+    #[test]
+    fn into_samples_vec_f32() {
+        let samples = vec![0.1f32, -0.2, 0.3];
+        let frame = AudioFrame::new(&samples, 16000);
+        assert!(matches!(frame.samples, Cow::Borrowed(_)));
+        assert_eq!(frame.samples(), &[0.1, -0.2, 0.3]);
+    }
+
+    #[test]
+    fn into_samples_array_f32() {
+        let samples = [0.1f32, -0.2, 0.3];
+        let frame = AudioFrame::new(&samples, 16000);
+        assert!(matches!(frame.samples, Cow::Borrowed(_)));
+        assert_eq!(frame.samples(), &[0.1, -0.2, 0.3]);
+    }
+
+    #[test]
+    fn into_samples_vec_i16() {
+        let samples: Vec<i16> = vec![0, 16384, i16::MIN];
+        let frame = AudioFrame::new(&samples, 16000);
+        assert!(matches!(frame.samples, Cow::Owned(_)));
+        let s = frame.samples();
+        assert!((s[0] - 0.0).abs() < f32::EPSILON);
+        assert!((s[1] - 0.5).abs() < 0.001);
+        assert!((s[2] - -1.0).abs() < f32::EPSILON);
+    }
+
+    #[test]
+    fn into_samples_array_i16() {
+        let samples: [i16; 3] = [0, 16384, i16::MIN];
+        let frame = AudioFrame::new(&samples, 16000);
+        assert!(matches!(frame.samples, Cow::Owned(_)));
+        let s = frame.samples();
+        assert!((s[0] - 0.0).abs() < f32::EPSILON);
+        assert!((s[1] - 0.5).abs() < 0.001);
+        assert!((s[2] - -1.0).abs() < f32::EPSILON);
+    }
 }
diff --git a/docs/02-test-coverage.md b/docs/02-test-coverage.md
new file mode 100644
index 0000000..342b26e
--- /dev/null
+++ b/docs/02-test-coverage.md
@@ -0,0 +1,37 @@
+# 02 — Test Coverage
+
+## Overview
+
+Code coverage is measured on every CI run using [`cargo-llvm-cov`](https://github.com/taiki-e/cargo-llvm-cov) and reported to [Codecov](https://codecov.io/gh/wavekat/wavekat-core).
+
+## How It Works
+
+The `coverage` job in `.github/workflows/ci.yml`:
+
+1. Installs `cargo-llvm-cov` via [`taiki-e/install-action`](https://github.com/taiki-e/install-action).
+2. Runs the full test suite with LLVM instrumentation across all features:
+   ```sh
+   cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
+   ```
+3. Uploads the LCOV report to Codecov.
+
+## Viewing Coverage
+
+- **Badge** — shown in `README.md`, reflects the latest `main` branch coverage.
+- **Codecov dashboard** — `https://codecov.io/gh/wavekat/wavekat-core` for line-by-line detail and PR diff coverage.
+
+## Setup (one-time)
+
+1. Sign in to [codecov.io](https://codecov.io) with your GitHub account.
+2. Enable the `wavekat/wavekat-core` repository.
+3. Add the `CODECOV_TOKEN` secret to the GitHub repository settings.
+
+## Running Locally
+
+```sh
+# Install dev tools once after cloning
+make install-dev
+
+# Generate an HTML report and open it
+make cov
+```