Clean up testing of get_appropriate_units

Use more descriptive test case names, and add a little macro to make
writing the tests less repetitive, per @eldruin's suggestions.

Author: alberdingk-thijm

Cargo.toml

@@ -5,7 +5,7 @@ authors = ["James O'Cull <[email protected]>",
           "Jonathan Pallant <[email protected]>",
           "Hannah McLaughlin <[email protected]>",
           "Danilo Bargen <[email protected]>",
-          "Tim Alberdingk Thijm <[email protected]>",
+          "Tim Alberdingk Thijm <tthijm@cs.princeton.edu>",
           ]
 documentation = "https://docs.rs/crate/measurements"
 repository = "https://github.com/thejpster/rust-measurements"

tests/get_appropriate_units.rs

@@ -0,0 +1,52 @@
+extern crate measurements;
+
+use measurements::{mass::Mass, test_utils::assert_almost_eq, Measurement};
+
+// Macro for testing `get_appropriate_units()`.
+// Specify the name of the test, the initial value (in kg) to be
+// passed in and the units that should be returned when
+// `get_appropriate_units()` is called.
+// An additional factor term may be given for cases when a
+// unit conversion takes place.
+macro_rules! test_from_kg {
+    ($name:ident, $value:expr, $unit:expr) => {
+        #[test]
+        fn $name() {
+            let mass = Mass::from_kilograms($value);
+            let (unit, v) = mass.get_appropriate_units();
+            assert_eq!(unit, $unit);
+            assert_almost_eq($value, v);
+        }
+    };
+    ($name:ident, $value:expr, $unit:expr, $factor:expr) => {
+        #[test]
+        fn $name() {
+            let mass = Mass::from_kilograms($value);
+            let (unit, v) = mass.get_appropriate_units();
+            assert_eq!(unit, $unit);
+            assert_almost_eq($value * $factor, v);
+        }
+    };
+}
+
+test_from_kg!(one_kg_keeps_unit, 1.0, "kg");
+test_from_kg!(minus_one_kg_keeps_unit, -1.0, "kg");
+test_from_kg!(more_than_one_kg_keeps_unit, 1.0 + 0.001, "kg");
+test_from_kg!(
+    less_than_one_kg_changes_unit_to_grams,
+    1.0 - 0.001,
+    "g",
+    1000.0
+);
+test_from_kg!(
+    one_thousand_kg_changes_unit_to_tonnes,
+    1000.0,
+    "tonnes",
+    0.001
+);
+test_from_kg!(
+    one_thousandth_of_kg_changes_unit_to_grams,
+    0.001,
+    "g",
+    1000.0
+);