diff --git a/Cargo.toml b/Cargo.toml
index 3f52e44..74e4831 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,3 +30,6 @@ confique-macro = { version = "=0.0.2", path = "macro" }
 serde = { version = "1", features = ["derive"] }
 serde_yaml = { version = "0.8", optional = true }
 toml = { version = "0.5", optional = true }
+
+[dev-dependencies]
+pretty_assertions = "1.2.1"
diff --git a/src/lib.rs b/src/lib.rs
index 52f8e37..67f8cfa 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -186,6 +186,9 @@ pub mod toml;
 #[cfg(feature = "yaml")]
 pub mod yaml;
 
+#[cfg(test)]
+mod test_utils;
+
 
 pub use serde;
 pub use self::{
diff --git a/src/test_utils/example1.rs b/src/test_utils/example1.rs
new file mode 100644
index 0000000..72a936a
--- /dev/null
+++ b/src/test_utils/example1.rs
@@ -0,0 +1,61 @@
+use std::{
+    net::IpAddr,
+    path::PathBuf,
+};
+
+use crate::Config;
+use crate as confique;
+
+#[derive(Debug, Config)]
+/// A sample configuration for our app.
+pub struct Conf {
+    /// Name of the website.
+    pub site_name: String,
+
+    /// Configurations related to the HTTP communication.
+    #[config(nested)]
+    pub http: Http,
+
+    /// Configuring the logging.
+    #[config(nested)]
+    pub log: LogConfig,
+}
+
+/// Configuring the HTTP server of our app.
+#[derive(Debug, Config)]
+pub struct Http {
+    /// The port the server will listen on.
+    #[config(env = "PORT")]
+    pub port: u16,
+
+    #[config(nested)]
+    pub headers: Headers,
+
+    /// The bind address of the server. Can be set to `0.0.0.0` for example, to
+    /// allow other users of the network to access the server.
+    #[config(default = "127.0.0.1")]
+    pub bind: IpAddr,
+}
+
+#[derive(Debug, Config)]
+pub struct Headers {
+    /// The header in which the reverse proxy specifies the username.
+    #[config(default = "x-username")]
+    pub username: String,
+
+    /// The header in which the reverse proxy specifies the display name.
+    #[config(default = "x-display-name")]
+    pub display_name: String,
+}
+
+
+#[derive(Debug, Config)]
+pub struct LogConfig {
+    /// If set to `true`, the app will log to stdout.
+    #[config(default = true)]
+    pub stdout: bool,
+
+    /// If this is set, the app will write logs to the given file. Of course,
+    /// the app has to have write access to that file.
+    pub file: Option<PathBuf>,
+}
diff --git a/src/test_utils/mod.rs b/src/test_utils/mod.rs
new file mode 100644
index 0000000..bea813d
--- /dev/null
+++ b/src/test_utils/mod.rs
@@ -0,0 +1,10 @@
+pub(crate) mod example1;
+
+
+macro_rules! include_format_output {
+    ($file:expr) => {
+        include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/tests/format-output/", $file))
+    };
+}
+
+pub(crate) use include_format_output;
diff --git a/src/toml.rs b/src/toml.rs
index a16ebfb..03ea1f8 100644
--- a/src/toml.rs
+++ b/src/toml.rs
@@ -184,3 +184,25 @@ impl fmt::Display for PrintExpr {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::test_utils::{self, include_format_output};
+    use super::{format, FormatOptions};
+    use pretty_assertions::assert_str_eq;
+
+    #[test]
+    fn default() {
+        let out = format::<test_utils::example1::Conf>(FormatOptions::default());
+        assert_str_eq!(&out, include_format_output!("1-default.toml"));
+    }
+
+    #[test]
+    fn no_comments() {
+        let out = format::<test_utils::example1::Conf>(FormatOptions {
+            comments: false,
+            indent: 0,
+        });
+        assert_str_eq!(&out, include_format_output!("1-no-comments.toml"));
+    }
+}
diff --git a/tests/format-output/1-default.toml b/tests/format-output/1-default.toml
new file mode 100644
index 0000000..5ce4692
--- /dev/null
+++ b/tests/format-output/1-default.toml
@@ -0,0 +1,43 @@
+# A sample configuration for our app.
+
+# Name of the website.
+#
+# Required! This value must be specified.
+#site_name =
+
+# Configurations related to the HTTP communication.
+
+[http]
+# The port the server will listen on.
+#
+# Required! This value must be specified.
+#port =
+
+# The bind address of the server. Can be set to `0.0.0.0` for example, to
+# allow other users of the network to access the server.
+#
+# Default value: "127.0.0.1"
+#bind = "127.0.0.1"
+
+[http.headers]
+# The header in which the reverse proxy specifies the username.
+#
+# Default value: "x-username"
+#username = "x-username"
+
+# The header in which the reverse proxy specifies the display name.
+#
+# Default value: "x-display-name"
+#display_name = "x-display-name"
+
+# Configuring the logging.
+
+[log]
+# If set to `true`, the app will log to stdout.
+#
+# Default value: true
+#stdout = true
+
+# If this is set, the app will write logs to the given file. Of course,
+# the app has to have write access to that file.
+#file =
diff --git a/tests/format-output/1-no-comments.toml b/tests/format-output/1-no-comments.toml
new file mode 100644
index 0000000..d8a0cea
--- /dev/null
+++ b/tests/format-output/1-no-comments.toml
@@ -0,0 +1,13 @@
+#site_name =
+
+[http]
+#port =
+#bind = "127.0.0.1"
+
+[http.headers]
+#username = "x-username"
+#display_name = "x-display-name"
+
+[log]
+#stdout = true
+#file =