Create solution.md

Author: ImVietnam

1-js/03-code-quality/05-testing-mocha/3-pow-test-wrong/solution.md

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+The test demonstrates one of the temptations a developer meets when writing tests.
+
+What we have here is actually 3 tests, but layed out as a single function with 3 asserts.
+
+Sometimes it's easier to write this way, but if an error occurs, it's much less obvious what went wrong.
+
+If an error happens in the middle of a complex execution flow, then we'll have to figure out the data at that point. We'll actually have to *debug the test*.
+
+It would be much better to break the test into multiple `it` blocks with clearly written inputs and outputs.
+
+Like this:
+```js
+describe("Raises x to power n", function() {
+  it("5 in the power of 1 equals 5", function() {
+    assert.equal(pow(5, 1), 5);
+  });
+
+  it("5 in the power of 2 equals 25", function() {
+    assert.equal(pow(5, 2), 25);
+  });
+
+  it("5 in the power of 3 equals 125", function() {
+    assert.equal(pow(5, 3), 125);
+  });
+});
+```
+
+We replaced the single `it` with `describe` and a group of `it` blocks. Now if something fails we would see clearly what the data was.
+
+Also we can isolate a single test and run it in standalone mode by writing `it.only` instead of `it`:
+
+
+```js
+describe("Raises x to power n", function() {
+  it("5 in the power of 1 equals 5", function() {
+    assert.equal(pow(5, 1), 5);
+  });
+
+*!*
+  // Mocha will run only this block
+  it.only("5 in the power of 2 equals 25", function() {
+    assert.equal(pow(5, 2), 25);
+  });
+*/!*
+
+  it("5 in the power of 3 equals 125", function() {
+    assert.equal(pow(5, 3), 125);
+  });
+});
+```