Testing best practices

Testing best practices

Add more best practices here!

Checking the size of a D3 Selection

The "length" of a D3 Selection is always 1, regardless of how many elements are in it:

d3.select().length; // 1, not 0

The correct way to check the size of the Selection is to assert that its size() is equal to a particular value:

assert.strictEquals(selection.size(), expectedSize, message);

Iterating over a d3 selection

Use

whateverSelection.selectAll("line").each(function() {
  let lineSelection = d3.select(this); // "this" refers to the DOM node inside the loop
});

Instead of hacky stuff like

whateverSelection.selectAll("line")[0].forEach((line) => {
  let lineSelection = d3.select(line);
});

Do not have svg.remove() inside an afterEach() block

That is because if something goes wrong with the test, we want to have the visual.

Minor

• Use plot.content() instead of plot._renderArea
• Make sure we use the it() semantically. It should read like a sentence. For example it("does not draw rectangles for invalid data points") instead of it("data points that are not valid, do not draw rectangles on the plot")

Suggestions:

These are just suggestions of best practices, slowly move them upwards as people agree. In add proposer & agreers to each to have a sense of what is okay

• Top level describes should act as category delimiters and should not have beforeEach(). That is because sometime we want to add a new, totally unrelated test to some category (say Plots.Line) and the beforeEach() does not make sense. Top Level means the title of the file (so for example "Plots" and "RectanglePlot" will be top level) (@acioara)