Split up tests

.travis.yml

@@ -1,7 +1,6 @@
 sudo: false
 language: node_js
 node_js:
-  - "4"
   - "6"
   - "8"
   - "10"
@@ -10,4 +9,4 @@ env:
     - BUILD_TIMEOUT=10000
 install: npm install --ignore-scripts
 before_install:
-  - if [[ $TRAVIS_NODE_VERSION -lt 7 ]]; then npm install --global npm@4; fi
+  - if [[ $TRAVIS_NODE_VERSION -lt 8 ]]; then npm install --global npm@5; fi

test/addExtension.test.js

@@ -0,0 +1,27 @@
+const assert = require( 'assert' );
+const addExtension = require( '..' ).addExtension;
+
+describe( 'addExtension', function () {
+	it( 'adds .js to an ID without an extension', function () {
+		assert.equal( addExtension( 'foo' ), 'foo.js' );
+	});
+
+	it( 'ignores file with existing extension', function () {
+		assert.equal( addExtension( 'foo.js' ), 'foo.js' );
+		assert.equal( addExtension( 'foo.json' ), 'foo.json' );
+	});
+
+	it( 'ignores file with trailing dot', function () {
+		assert.equal( addExtension( 'foo.' ), 'foo.' );
+	});
+
+	it( 'ignores leading .', function () {
+		assert.equal( addExtension( './foo' ), './foo.js' );
+		assert.equal( addExtension( './foo.js' ), './foo.js' );
+	});
+
+	it( 'adds a custom extension', function () {
+		assert.equal( addExtension( 'foo', '.wut' ), 'foo.wut' );
+		assert.equal( addExtension( 'foo.lol', '.wut' ), 'foo.lol' );
+	});
+});