Controlling Tests

Command Line Options either go to:
1. cargo test - Run this command for help, cargo test --help
2. The resulting test binary - Run this command for help, cargo test -- --help.
In simple terms, if you want to pass something into tests binary you'll have to seperate them with --.

By default, Rust runs tests in different threads.
In case the test depends on each other. For example, tests perform read, write, and assert to a same file. If run concurrently, the file will get corrupt and the tests might fail.
To run tests on a single thread, one by one we can do it by:
```
cargo test -- --test-threads=1
```
This command will prevent parallelism, though the tests will take longer to run but it'll save us from the above problem.

By default, when we run cargo test, the compiler never prints the statements.
To display print statements we can run this command:
```
cargo test -- --show-output
```

To run specific tests either 1 or more, we can do that by specifying the name of test.
- For One Test:
```
cargo test <name-of-test>
```
- For more than one test (e.g. add_two, add_three, then substring add):
```
cargo test <substring-of-tests-name>
```
When we run specific tests, the remaining tests will fall into the category of filtered out, you may see that in the logs.
Also note that the module in which a test appears becomes part of the test’s name, so we can run all the tests in a module by filtering on the module’s name.

Instead of filtering tests, you may like to ignore the tests by adding #[ignore] attribute above each test that you'd like to ignore.
Now, you may use the following commands to run the tests.
- To run the tests ignoring ones that use #[ignore] attribute:
```
cargo test
```
- To run only the ignored tests:
```
cargo test -- --ignored
```
- To run both ignored and not ignored tests:
```
cargo test -- --include-ignored
```