Dedicated function for inverting a transform without modifying the source

test/spec/ol/transform.test.js

@@ -9,6 +9,7 @@ import {
   multiply,
   compose,
   invert,
+  makeInverse,
   apply
 } from '../../../src/ol/transform.js';
 
@@ -110,13 +111,39 @@ describe('ol.transform', function() {
 
   describe('invert()', function() {
     it('inverts a transform', function() {
-      let transform = [1, 0, 1, 0, 1, 0];
-      expect(function() {
-        invert(transform);
-      }).to.throwException();
-      transform = [1, 1, 1, 2, 2, 0];
+      const transform = [1, 1, 1, 2, 2, 0];
       expect(invert(transform)).to.eql([2, -1, -1, 1, -4, 2]);
-      expect(transform).to.eql([2, -1, -1, 1, -4, 2]);
+    });
+
+    it('throws if the transform cannot be inverted', function() {
+      const indeterminant = [1, 0, 1, 0, 1, 0];
+      expect(function() {
+        invert(indeterminant);
+      }).to.throwException();
+    });
+
+    it('modifies the source', function() {
+      const source = [1, 1, 1, 2, 2, 0];
+      const inverted = invert(source);
+      expect(inverted).to.eql([2, -1, -1, 1, -4, 2]);
+      expect(source).to.be(inverted);
+    });
+  });
+
+  describe('makeInverse()', function() {
+    it('makes the target the inverse of the source', function() {
+      const source = [1, 1, 1, 2, 2, 0];
+      const target = [1, 0, 0, 1, 0, 0];
+      makeInverse(source, target);
+      expect(source).to.eql([1, 1, 1, 2, 2, 0]);
+      expect(target).to.eql([2, -1, -1, 1, -4, 2]);
+    });
+
+    it('returns the target', function() {
+      const source = [1, 1, 1, 2, 2, 0];
+      const target = [1, 0, 0, 1, 0, 0];
+      const inverted = makeInverse(source, target);
+      expect(target).to.be(inverted);
     });
   });