Add some exercises about tests!

README.md

@@ -39,6 +39,18 @@ If you need more help or would like to compare solutions, you can ask in [#rust
 - ["primitive_types1.rs"](http://play.rust-lang.org/?code=%2F%2F+Fill+in+the+rest+of+the+line+that+has+code+missing%21%0A%2F%2F+No+hints%2C+there%27s+no+tricks%2C+just+get+used+to+typing+these+%3A%29%0A%0Afn+main%28%29+%7B%0A++++%2F%2F+Booleans+%28%60bool%60%29%0A%0A++++let+is_morning+%3D+true%3B%0A++++if+is_morning+%7B%0A++++++++println%21%28%22Good+morning%21%22%29%3B%0A++++%7D%0A%0A++++let+%2F%2F+Finish+the+rest+of+this+line+like+the+example%21+Or+make+it+be+false%21%0A++++if+is_evening+%7B%0A++++++++println%21%28%22Good+evening%21%22%29%3B%0A++++%7D%0A%7D%0A)
 - ["primitive_types2.rs"](http://play.rust-lang.org/?code=%2F%2F+Fill+in+the+rest+of+the+line+that+has+code+missing%21%0A%2F%2F+No+hints%2C+there%27s+no+tricks%2C+just+get+used+to+typing+these+%3A%29%0A%0Afn+main%28%29+%7B%0A++++%2F%2F+Characters+%28%60char%60%29%0A%0A++++let+my_first_initial+%3D+%27C%27%3B%0A++++if+my_first_initial.is_alphabetic%28%29+%7B%0A++++++++println%21%28%22Alphabetical%21%22%29%3B%0A++++%7D+else+if+my_first_initial.is_numeric%28%29+%7B%0A++++++++println%21%28%22Numerical%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Neither+alphabetic+nor+numeric%21%22%29%3B%0A++++%7D%0A%0A++++let+%2F%2F+Finish+this+line+like+the+example%21+What%27s+your+favorite+character%3F%0A++++%2F%2F+Try+a+letter%2C+try+a+number%2C+try+a+special+character%2C+try+a+character%0A++++%2F%2F+from+a+different+language+than+your+own%2C+try+an+emoji%21%0A++++if+your_character.is_alphabetic%28%29+%7B%0A++++++++println%21%28%22Alphabetical%21%22%29%3B%0A++++%7D+else+if+your_character.is_numeric%28%29+%7B%0A++++++++println%21%28%22Numerical%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Neither+alphabetic+nor+numeric%21%22%29%3B%0A++++%7D%0A%7D%0A)
 
+### Tests
+
+Going out of order from the Syntax and Semantics section of the book to cover tests-- many of the
+following exercises will ask you to make tests pass!
+
+[Testing chapter from the Effective Rust section of the book](https://doc.rust-lang.org/stable/book/testing.html)
+
+- ["tests1.rs"](http://play.rust-lang.org/?code=%2F%2F+This+test+has+a+problem+with+it+--+make+the+test+compile%21+Make+the+test%0A%2F%2F+pass%21+Make+the+test+fail%21+Scroll+down+for+hints+%3A%29%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++%23%5Btest%5D%0A++++fn+you_can_assert%28%29+%7B%0A++++++++assert%21%28%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+You+don%27t+even+need+to+write+any+code+to+test+--+you+can+just+test+values+and+run+that%2C+even%0A%2F%2F+though+you+wouldn%27t+do+that+in+real+life+%3A%29+%60assert%21%60+is+a+macro+that+needs+an+argument.%0A%2F%2F+Depending+on+the+value+of+the+argument%2C+%60assert%21%60+will+do+nothing+%28in+which+case+the+test+will%0A%2F%2F+pass%29+or+%60assert%21%60+will+panic+%28in+which+case+the+test+will+fail%29.+So+try+giving+different+values%0A%2F%2F+to+%60assert%21%60+and+see+which+ones+compile%2C+which+ones+pass%2C+and+which+ones+fail+%3A%29%0A)
+- ["tests2.rs"](http://play.rust-lang.org/?code=%2F%2F+This+test+has+a+problem+with+it+--+make+the+test+compile%21+Make+the+test%0A%2F%2F+pass%21+Make+the+test+fail%21+Scroll+down+for+hints+%3A%29%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++%23%5Btest%5D%0A++++fn+you_can_assert_eq%28%29+%7B%0A++++++++assert_eq%21%28%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Like+the+previous+exercise%2C+you+don%27t+need+to+write+any+code+to+get+this+test+to+compile+and%0A%2F%2F+run.+%60assert_eq%21%60+is+a+macro+that+takes+two+arguments+and+compares+them.+Try+giving+it+two%0A%2F%2F+values+that+are+equal%21+Try+giving+it+two+arguments+that+are+different%21+Try+giving+it+two+values%0A%2F%2F+that+are+of+different+types%21+Try+switching+which+argument+comes+first+and+which+comes+second%21%0A)
+- ["tests3.rs"](http://play.rust-lang.org/?code=%2F%2F+This+test+isn%27t+testing+our+function+--+make+it+do+that+in+such+a+way+that%0A%2F%2F+the+test+passes.+Then+write+a+second+test+that+tests+that+we+get+the+result%0A%2F%2F+we+expect+to+get+when+we+call+%60is_even%285%29%60.+Scroll+down+for+hints%21%0A%0Apub+fn+is_even%28num%3A+i32%29+-%3E+bool+%7B%0A++++num+%25+2+%3D%3D+0%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%23%5Btest%5D%0A++++fn+is_true_when_even%28%29+%7B%0A++++++++assert%21%28false%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+You+can+call+a+function+right+where+you%27re+passing+arguments+to+%60assert%21%60+--+so+you+could+do%0A%2F%2F+something+like+%60assert%21%28having_fun%28%29%29%60.+If+you+want+to+check+that+you+indeed+get+false%2C+you%0A%2F%2F+can+negate+the+result+of+what+you%27re+doing+using+%60%21%60%2C+like+%60assert%21%28%21having_fun%28%29%29%60.%0A)
+- ["tests4.rs"](http://play.rust-lang.org/?code=%2F%2F+This+test+isn%27t+testing+our+function+--+make+it+do+that+in+such+a+way+that%0A%2F%2F+the+test+passes.+Then+write+a+second+test+that+tests+that+we+get+the+result%0A%2F%2F+we+expect+to+get+when+we+call+%60times_two%60+with+a+negative+number.%0A%2F%2F+No+hints%2C+you+can+do+this+%3A%29%0A%0Apub+fn+times_two%28num%3A+i32%29+-%3E+i32+%7B%0A++++num+*+2%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%23%5Btest%5D%0A++++fn+returns_twice_of_positive_numbers%28%29+%7B%0A++++++++assert_eq%21%284%2C+4%29%3B%0A++++%7D%0A%7D%0A)
+
 ### Strings
 
 [Relevant chapter in The Rust Programming Language](https://doc.rust-lang.org/stable/book/strings.html)

tests/tests1.rs

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+// This test has a problem with it -- make the test compile! Make the test
+// pass! Make the test fail! Scroll down for hints :)
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+#[cfg(test)]
+mod tests {
+    #[test]
+    fn you_can_assert() {
+        assert!();
+    }
+}
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+// You don't even need to write any code to test -- you can just test values and run that, even
+// though you wouldn't do that in real life :) `assert!` is a macro that needs an argument.
+// Depending on the value of the argument, `assert!` will do nothing (in which case the test will
+// pass) or `assert!` will panic (in which case the test will fail). So try giving different values
+// to `assert!` and see which ones compile, which ones pass, and which ones fail :)

tests/tests2.rs

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+// This test has a problem with it -- make the test compile! Make the test
+// pass! Make the test fail! Scroll down for hints :)
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn you_can_assert_eq() {
+        assert_eq!();
+    }
+}
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+// Like the previous exercise, you don't need to write any code to get this test to compile and
+// run. `assert_eq!` is a macro that takes two arguments and compares them. Try giving it two
+// values that are equal! Try giving it two arguments that are different! Try giving it two values
+// that are of different types! Try switching which argument comes first and which comes second!

tests/tests3.rs

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+// This test isn't testing our function -- make it do that in such a way that
+// the test passes. Then write a second test that tests that we get the result
+// we expect to get when we call `is_even(5)`. Scroll down for hints!
+
+pub fn is_even(num: i32) -> bool {
+    num % 2 == 0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn is_true_when_even() {
+        assert!(false);
+    }
+}
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+// You can call a function right where you're passing arguments to `assert!` -- so you could do
+// something like `assert!(having_fun())`. If you want to check that you indeed get false, you
+// can negate the result of what you're doing using `!`, like `assert!(!having_fun())`.

tests/tests4.rs

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+// This test isn't testing our function -- make it do that in such a way that
+// the test passes. Then write a second test that tests that we get the result
+// we expect to get when we call `times_two` with a negative number.
+// No hints, you can do this :)
+
+pub fn times_two(num: i32) -> i32 {
+    num * 2
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn returns_twice_of_positive_numbers() {
+        assert_eq!(4, 4);
+    }
+}