diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index aed47654f..2c5ee4438 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -15,6 +15,7 @@ env:
   CARGO_NET_RETRY: 10
   CARGO_TERM_COLOR: always
   RUSTUP_MAX_RETRIES: 10
+  PYTHON_VERSION: "3.12"
 
 jobs:
   cargo-fmt:
@@ -47,6 +48,10 @@ jobs:
     name: "cargo test | ${{ matrix.os }}"
     steps:
       - uses: actions/checkout@v4
+      - name: "Install Python"
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install cargo insta"
diff --git a/Cargo.lock b/Cargo.lock
index 130e83e7d..367f04bf7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1308,6 +1308,7 @@ dependencies = [
  "console",
  "lazy_static",
  "linked-hash-map",
+ "regex",
  "serde",
  "similar",
  "yaml-rust",
@@ -2060,6 +2061,7 @@ dependencies = [
  "futures",
  "gourgeist",
  "indicatif",
+ "insta",
  "insta-cmd",
  "install-wheel-rs",
  "itertools",
diff --git a/crates/puffin-cli/Cargo.toml b/crates/puffin-cli/Cargo.toml
index e13fc2050..6a9609078 100644
--- a/crates/puffin-cli/Cargo.toml
+++ b/crates/puffin-cli/Cargo.toml
@@ -48,4 +48,11 @@ which = { workspace = true }
 assert_cmd = { version = "2.0.8" }
 assert_fs = { version = "1.0.13" }
 insta-cmd = { version = "0.4.0" }
+insta = { version = "1.34.0", features = ["filters"] }
 predicates = { version = "3.0.4" }
+
+[features]
+# Introduces a dependency on a local Python installation.
+python = []
+# Introduces a dependency on PyPI.
+pypi = []
diff --git a/crates/puffin-cli/src/main.rs b/crates/puffin-cli/src/main.rs
index 37a526a62..366dcc066 100644
--- a/crates/puffin-cli/src/main.rs
+++ b/crates/puffin-cli/src/main.rs
@@ -32,6 +32,10 @@ struct Cli {
     /// Avoid reading from or writing to the cache.
     #[arg(global = true, long, short)]
     no_cache: bool,
+
+    /// Path to the cache directory.
+    #[arg(global = true, long, env = "PUFFIN_CACHE_DIR")]
+    cache_dir: Option<PathBuf>,
 }
 
 #[derive(Subcommand)]
@@ -133,9 +137,17 @@ async fn main() -> ExitCode {
         printer::Printer::Default
     };
 
+    let project_dirs = ProjectDirs::from("", "", "puffin");
+    let cache_dir = (!cli.no_cache)
+        .then(|| {
+            cli.cache_dir
+                .as_deref()
+                .or_else(|| project_dirs.as_ref().map(ProjectDirs::cache_dir))
+        })
+        .flatten();
+
     let result = match cli.command {
         Commands::PipCompile(args) => {
-            let dirs = ProjectDirs::from("", "", "puffin");
             let requirements = args
                 .src_file
                 .into_iter()
@@ -151,59 +163,30 @@ async fn main() -> ExitCode {
                 &constraints,
                 args.output_file.as_deref(),
                 args.resolution.unwrap_or_default(),
-                dirs.as_ref()
-                    .map(ProjectDirs::cache_dir)
-                    .filter(|_| !cli.no_cache),
+                cache_dir,
                 printer,
             )
             .await
         }
         Commands::PipSync(args) => {
-            let dirs = ProjectDirs::from("", "", "puffin");
             let sources = args
                 .src_file
                 .into_iter()
                 .map(RequirementsSource::from)
                 .collect::<Vec<_>>();
-            commands::pip_sync(
-                &sources,
-                dirs.as_ref()
-                    .map(ProjectDirs::cache_dir)
-                    .filter(|_| !cli.no_cache),
-                printer,
-            )
-            .await
+            commands::pip_sync(&sources, cache_dir, printer).await
         }
         Commands::PipUninstall(args) => {
-            let dirs = ProjectDirs::from("", "", "puffin");
             let sources = args
                 .package
                 .into_iter()
                 .map(RequirementsSource::from)
                 .chain(args.requirement.into_iter().map(RequirementsSource::from))
                 .collect::<Vec<_>>();
-            commands::pip_uninstall(
-                &sources,
-                dirs.as_ref()
-                    .map(ProjectDirs::cache_dir)
-                    .filter(|_| !cli.no_cache),
-                printer,
-            )
-            .await
-        }
-        Commands::Clean => {
-            let dirs = ProjectDirs::from("", "", "puffin");
-            commands::clean(dirs.as_ref().map(ProjectDirs::cache_dir), printer).await
-        }
-        Commands::Freeze => {
-            let dirs = ProjectDirs::from("", "", "puffin");
-            commands::freeze(
-                dirs.as_ref()
-                    .map(ProjectDirs::cache_dir)
-                    .filter(|_| !cli.no_cache),
-                printer,
-            )
+            commands::pip_uninstall(&sources, cache_dir, printer).await
         }
+        Commands::Clean => commands::clean(cache_dir, printer).await,
+        Commands::Freeze => commands::freeze(cache_dir, printer),
         Commands::Venv(args) => commands::venv(&args.name, args.python.as_deref(), printer).await,
         Commands::Add(args) => commands::add(&args.name, printer),
         Commands::Remove(args) => commands::remove(&args.name, printer),
diff --git a/crates/puffin-cli/tests/pip_sync.rs b/crates/puffin-cli/tests/pip_sync.rs
new file mode 100644
index 000000000..668170760
--- /dev/null
+++ b/crates/puffin-cli/tests/pip_sync.rs
@@ -0,0 +1,387 @@
+#![cfg(all(feature = "python", feature = "pypi"))]
+
+use std::process::Command;
+
+use anyhow::Result;
+use assert_cmd::prelude::*;
+use assert_fs::prelude::*;
+use insta_cmd::_macro_support::insta;
+use insta_cmd::{assert_cmd_snapshot, get_cargo_bin};
+
+const BIN_NAME: &str = "puffin";
+
+#[test]
+fn missing_requirements_txt() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let requirements_txt = temp_dir.child("requirements.txt");
+
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .arg("pip-sync")
+        .arg("requirements.txt")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir));
+
+    requirements_txt.assert(predicates::path::missing());
+
+    Ok(())
+}
+
+#[test]
+fn missing_venv() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = temp_dir.child(".venv");
+
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .arg("pip-sync")
+        .arg("requirements.txt")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .env("VIRTUAL_ENV", venv.as_os_str())
+        .current_dir(&temp_dir));
+
+    venv.assert(predicates::path::missing());
+
+    Ok(())
+}
+
+/// Install a package into a virtual environment.
+#[test]
+fn install() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = temp_dir.child(".venv");
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+    venv.assert(predicates::path::is_dir());
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("MarkupSafe==2.1.3")?;
+
+    insta::with_settings!({
+        filters => vec![
+            (r"\d+ms", "[TIME]"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-sync")
+            .arg("requirements.txt")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir));
+    });
+
+    Command::new(venv.join("bin").join("python"))
+        .arg("-c")
+        .arg("import markupsafe")
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    Ok(())
+}
+
+/// Install multiple packages into a virtual environment.
+#[test]
+fn install_many() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = temp_dir.child(".venv");
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+    venv.assert(predicates::path::is_dir());
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("MarkupSafe==2.1.3\ntomli==2.0.1")?;
+
+    insta::with_settings!({
+        filters => vec![
+            (r"\d+ms", "[TIME]"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-sync")
+            .arg("requirements.txt")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir));
+    });
+
+    Command::new(venv.join("bin").join("python"))
+        .arg("-c")
+        .arg("import markupsafe; import tomli")
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    Ok(())
+}
+
+/// Attempt to install an already-installed package into a virtual environment.
+#[test]
+fn noop() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = temp_dir.child(".venv");
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+    venv.assert(predicates::path::is_dir());
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("MarkupSafe==2.1.3")?;
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("pip-sync")
+        .arg("requirements.txt")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .env("VIRTUAL_ENV", venv.as_os_str())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    insta::with_settings!({
+        filters => vec![
+            (r"\d+ms", "[TIME]"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-sync")
+            .arg("requirements.txt")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir));
+    });
+
+    Command::new(venv.join("bin").join("python"))
+        .arg("-c")
+        .arg("import markupsafe")
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    Ok(())
+}
+
+/// Install a package into a virtual environment, then install the same package into a different
+/// virtual environment.
+#[test]
+fn link() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = temp_dir.child(".venv");
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+    venv.assert(predicates::path::is_dir());
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("MarkupSafe==2.1.3")?;
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("pip-sync")
+        .arg("requirements.txt")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .env("VIRTUAL_ENV", venv.as_os_str())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    let venv = temp_dir.child(".venv");
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+    venv.assert(predicates::path::is_dir());
+
+    insta::with_settings!({
+        filters => vec![
+            (r"\d+ms", "[TIME]"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-sync")
+            .arg("requirements.txt")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir));
+    });
+
+    Command::new(venv.join("bin").join("python"))
+        .arg("-c")
+        .arg("import markupsafe")
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    Ok(())
+}
+
+/// Install a package into a virtual environment, then sync the virtual environment with a
+/// different requirements file.
+#[test]
+fn add_remove() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = temp_dir.child(".venv");
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+    venv.assert(predicates::path::is_dir());
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("MarkupSafe==2.1.3")?;
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("pip-sync")
+        .arg("requirements.txt")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .env("VIRTUAL_ENV", venv.as_os_str())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("tomli==2.0.1")?;
+
+    insta::with_settings!({
+        filters => vec![
+            (r"\d+ms", "[TIME]"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-sync")
+            .arg("requirements.txt")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir));
+    });
+
+    Command::new(venv.join("bin").join("python"))
+        .arg("-c")
+        .arg("import tomli")
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    Command::new(venv.join("bin").join("python"))
+        .arg("-c")
+        .arg("import markupsafe")
+        .current_dir(&temp_dir)
+        .assert()
+        .failure();
+
+    Ok(())
+}
+
+/// Install a package into a virtual environment, then install a second package into the same
+/// virtual environment.
+#[test]
+fn install_sequential() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = temp_dir.child(".venv");
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+    venv.assert(predicates::path::is_dir());
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("MarkupSafe==2.1.3")?;
+
+    Command::new(get_cargo_bin(BIN_NAME))
+        .arg("pip-sync")
+        .arg("requirements.txt")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .env("VIRTUAL_ENV", venv.as_os_str())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    let requirements_txt = temp_dir.child("requirements.txt");
+    requirements_txt.touch()?;
+    requirements_txt.write_str("MarkupSafe==2.1.3\ntomli==2.0.1")?;
+
+    insta::with_settings!({
+        filters => vec![
+            (r"\d+ms", "[TIME]"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-sync")
+            .arg("requirements.txt")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir));
+    });
+
+    Command::new(venv.join("bin").join("python"))
+        .arg("-c")
+        .arg("import markupsafe; import tomli")
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    Ok(())
+}
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__add_remove.snap b/crates/puffin-cli/tests/snapshots/pip_sync__add_remove.snap
new file mode 100644
index 000000000..173550a3a
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__add_remove.snap
@@ -0,0 +1,25 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+    - "--cache-dir"
+    - /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpdWoKpL
+  env:
+    VIRTUAL_ENV: /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpVhsDyT/.venv
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Resolved 1 package in [TIME]
+Downloaded 1 package in [TIME]
+Unzipped 1 package in [TIME]
+Uninstalled 1 package in [TIME]
+Installed 1 package in [TIME]
+ - markupsafe@2.1.3
+ + tomli@2.0.1
+
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__install.snap b/crates/puffin-cli/tests/snapshots/pip_sync__install.snap
new file mode 100644
index 000000000..a692a67c7
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__install.snap
@@ -0,0 +1,20 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+    - "--no-cache"
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Resolved 1 package in [TIME]
+Downloaded 1 package in [TIME]
+Unzipped 1 package in [TIME]
+Installed 1 package in [TIME]
+ + markupsafe@2.1.3
+
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__install_many.snap b/crates/puffin-cli/tests/snapshots/pip_sync__install_many.snap
new file mode 100644
index 000000000..7400aa8f6
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__install_many.snap
@@ -0,0 +1,24 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+    - "--cache-dir"
+    - /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpoqh2hP
+  env:
+    VIRTUAL_ENV: /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpZCdve2/.venv
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Resolved 2 packages in [TIME]
+Downloaded 2 packages in [TIME]
+Unzipped 2 packages in [TIME]
+Installed 2 packages in [TIME]
+ + markupsafe@2.1.3
+ + tomli@2.0.1
+
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__install_sequential.snap b/crates/puffin-cli/tests/snapshots/pip_sync__install_sequential.snap
new file mode 100644
index 000000000..1109c7b07
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__install_sequential.snap
@@ -0,0 +1,23 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+    - "--cache-dir"
+    - /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpWxh1hG
+  env:
+    VIRTUAL_ENV: /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpUUUwuX/.venv
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Resolved 1 package in [TIME]
+Downloaded 1 package in [TIME]
+Unzipped 1 package in [TIME]
+Installed 1 package in [TIME]
+ + tomli@2.0.1
+
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__link.snap b/crates/puffin-cli/tests/snapshots/pip_sync__link.snap
new file mode 100644
index 000000000..652bd9024
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__link.snap
@@ -0,0 +1,20 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+    - "--cache-dir"
+    - /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmprConY4
+  env:
+    VIRTUAL_ENV: /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpxukjZu/.venv
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Installed 1 package in [TIME]
+ + markupsafe@2.1.3
+
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__missing_requirements_txt.snap b/crates/puffin-cli/tests/snapshots/pip_sync__missing_requirements_txt.snap
new file mode 100644
index 000000000..125f702f1
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__missing_requirements_txt.snap
@@ -0,0 +1,16 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+---
+success: false
+exit_code: 2
+----- stdout -----
+
+----- stderr -----
+error: failed to open file `requirements.txt`
+  Caused by: No such file or directory (os error 2)
+
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__missing_venv.snap b/crates/puffin-cli/tests/snapshots/pip_sync__missing_venv.snap
new file mode 100644
index 000000000..061a17cdd
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__missing_venv.snap
@@ -0,0 +1,18 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+  env:
+    VIRTUAL_ENV: /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpvJQh45/.venv
+---
+success: false
+exit_code: 2
+----- stdout -----
+
+----- stderr -----
+error: failed to open file `requirements.txt`
+  Caused by: No such file or directory (os error 2)
+
diff --git a/crates/puffin-cli/tests/snapshots/pip_sync__noop.snap b/crates/puffin-cli/tests/snapshots/pip_sync__noop.snap
new file mode 100644
index 000000000..6c0a12c5b
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/pip_sync__noop.snap
@@ -0,0 +1,19 @@
+---
+source: crates/puffin-cli/tests/pip_sync.rs
+info:
+  program: puffin
+  args:
+    - pip-sync
+    - requirements.txt
+    - "--cache-dir"
+    - /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpEvtFoB
+  env:
+    VIRTUAL_ENV: /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpYZqcOB/.venv
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Audited 1 package in [TIME]
+
diff --git a/crates/puffin-cli/tests/snapshots/venv__create_venv.snap b/crates/puffin-cli/tests/snapshots/venv__create_venv.snap
new file mode 100644
index 000000000..bcfe75d21
--- /dev/null
+++ b/crates/puffin-cli/tests/snapshots/venv__create_venv.snap
@@ -0,0 +1,16 @@
+---
+source: crates/puffin-cli/tests/venv.rs
+info:
+  program: puffin
+  args:
+    - venv
+    - /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpn0fxWx/.venv
+---
+success: true
+exit_code: 0
+----- stdout -----
+
+----- stderr -----
+Using Python interpreter: /usr/bin/python3
+Creating virtual environment at: /home/ferris/project/.venv
+
diff --git a/crates/puffin-cli/tests/venv.rs b/crates/puffin-cli/tests/venv.rs
new file mode 100644
index 000000000..69fe06bd4
--- /dev/null
+++ b/crates/puffin-cli/tests/venv.rs
@@ -0,0 +1,32 @@
+#![cfg(feature = "python")]
+
+use std::process::Command;
+
+use anyhow::Result;
+use assert_fs::prelude::*;
+use insta_cmd::_macro_support::insta;
+use insta_cmd::{assert_cmd_snapshot, get_cargo_bin};
+
+const BIN_NAME: &str = "puffin";
+
+#[test]
+fn create_venv() -> Result<()> {
+    let tempdir = assert_fs::TempDir::new()?;
+    let venv = tempdir.child(".venv");
+
+    insta::with_settings!({
+        filters => vec![
+            (r"Using Python interpreter: .+", "Using Python interpreter: /usr/bin/python3"),
+            (tempdir.to_str().unwrap(), "/home/ferris/project"),
+        ]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("venv")
+            .arg(venv.as_os_str())
+            .current_dir(&tempdir));
+    });
+
+    venv.assert(predicates::path::is_dir());
+
+    Ok(())
+}
diff --git a/crates/puffin-resolver/Cargo.toml b/crates/puffin-resolver/Cargo.toml
index 25443a650..c9bbc936d 100644
--- a/crates/puffin-resolver/Cargo.toml
+++ b/crates/puffin-resolver/Cargo.toml
@@ -36,3 +36,7 @@ waitmap = { workspace = true }
 [dev-dependencies]
 once_cell = { version = "1.18.0" }
 insta = { version = "1.34.0" }
+
+[features]
+# Introduces a dependency on PyPI.
+pypi = []
diff --git a/crates/puffin-resolver/tests/resolver.rs b/crates/puffin-resolver/tests/resolver.rs
index da5e7c737..fb7c89a94 100644
--- a/crates/puffin-resolver/tests/resolver.rs
+++ b/crates/puffin-resolver/tests/resolver.rs
@@ -1,3 +1,5 @@
+#![cfg(feature = "pypi")]
+
 //! Integration tests for the resolver. These tests rely on a live network connection, and hit
 //! `PyPI` directly.