Prevent dead-code-elimination before coverage

.travis.yml

@@ -9,6 +9,10 @@ matrix:
   allow_failures:
     - rust: nightly
 
+env:
+  global:
+  - RUSTFLAGS="-C link-dead-code"
+
 before_install:
   - sudo apt-get update
 

README.md

@@ -37,6 +37,11 @@ for each test executable and store the results in separate directories.**
 Codecov will automatically find and upload the cobertura.xml files and
 merge the coverage for you.
 
+Note that setting the environment variable `RUSTFLAGS="-C link-dead-code"`
+during tests build may improve coverage accuracy by preventing dead-code elimination.
+Do not set this variable when creating release builds since it will increase
+binary size.
+
 After you've run the tests and created a cobertura.xml report, you can
 use [the Codecov global uploader][4] to push that report to Codecov.
 See below for further details.
@@ -71,6 +76,10 @@ matrix:
   allow_failures:
     - rust: nightly
 
+env:
+  global:
+  - RUSTFLAGS="-C link-dead-code"
+
 before_install:
   - sudo apt-get update
 

src/lib.rs

@@ -35,6 +35,17 @@ pub fn which(face: &str) -> &'static str {
     }
 }
 
+/// This function is not called during tests, so it will be considered dead code.
+/// By default, and because of dead-code elimination it won't be reported as uncovered
+/// since the function will be removed from executable.
+/// This is accounted for in the Travis configuration by passing the compiler flag
+/// `-C link-dead-code` when building the tests. This flag disables dead code
+/// elimination and allows this function to be reported correctly.
+pub fn not_called() {
+    println!("This is dead code");
+    unreachable!();
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;