Consistently use tests as the module name for tests (again) (heroku…

…#342)

Since we should be consistent, and the idiomatic naming is `tests`:
https://doc.rust-lang.org/book/ch11-03-test-organization.html#unit-tests
https://doc.rust-lang.org/rust-by-example/testing/unit_testing.html

Fixes new instances added since heroku#191.

examples/execd/src/bin/dice_roller.rs

@@ -36,7 +36,7 @@ fn roll_dice(amount: usize, sides: u32) -> u32 {
 }
 
 #[cfg(test)]
-mod test {
+mod tests {
     use super::*;
 
     #[test]

libcnb-test/src/app.rs

@@ -27,7 +27,7 @@ pub enum PrepareAppError {
 }
 
 #[cfg(test)]
-mod test {
+mod tests {
     use std::collections::HashMap;
     use std::path::PathBuf;
     use tempfile::tempdir;

libcnb-test/src/container_port_mapping.rs

@@ -103,7 +103,7 @@ pub(crate) fn port_mapped_container_config(ports: &[u16]) -> bollard::container:
 }
 
 #[cfg(test)]
-mod test {
+mod tests {
     use super::*;
     use bollard::models::PortMap;
 

libcnb-test/src/macros.rs

@@ -48,7 +48,7 @@ right: `{:?}`: {}"#,
 }
 
 #[cfg(test)]
-mod test {
+mod tests {
     #[test]
     fn simple() {
         assert_contains!("Hello World!", "World");

libcnb-test/src/pack.rs

@@ -94,7 +94,7 @@ impl From<PackBuildCommand> for Command {
 }
 
 #[cfg(test)]
-mod test {
+mod tests {
     use super::*;
     use std::ffi::OsStr;
 

libcnb/src/layer/mod.rs

@@ -4,7 +4,7 @@ mod handling;
 mod public_interface;
 
 #[cfg(test)]
-mod test;
+mod tests;
 
 pub(crate) use handling::*;
 pub use public_interface::*;