Introduce unit test based on image comparison (chartjs#3988)

Attempt to make easier the creation of unit tests that check the drawing output. Until now, this was done by checking calls on a 'fake' context, which is hard to maintain (need to update pixel values by hands) and also not reliable when optimizing code (i.e. different calls sequence but same result).

As of now, it's possible to define 'auto' tests based on JSON/PNG fixtures: chart is generated from the JSON file and compared to the associated PNG image. The image diff is done using `pixelmatch`. As an example (and in preparation of the `filler` plugin), add auto tests for the line element `fill` options.

gulpfile.js

@@ -171,6 +171,8 @@ function validHTMLTask() {
 
 function startTest() {
   return [
+    {pattern: './test/fixtures/**/*.json', included: false},
+    {pattern: './test/fixtures/**/*.png', included: false},
     './node_modules/moment/min/moment.min.js',
     './test/jasmine.index.js',
     './src/**/*.js',

package.json

@@ -37,6 +37,7 @@
     "karma-jasmine": "^1.1.0",
     "karma-jasmine-html-reporter": "^0.2.2",
     "merge-stream": "^1.0.0",
+    "pixelmatch": "^4.0.2",
     "vinyl-source-stream": "^1.1.0",
     "watchify": "^3.7.0",
     "yargs": "^5.0.0"

test/fixtures/element.line/fill-line-bottom-span.json

@@ -0,0 +1,55 @@
+{
+    "config": {
+        "type": "line",
+        "data": {
+            "labels": ["0", "1", "2", "3", "4", "5", "6", "7", "8"],
+            "datasets": [{
+                "backgroundColor": "rgba(0, 0, 255, 0.25)",
+                "data": [null, null, 2, 3, 4, -4, -2, 1, 0]
+            }, {
+                "backgroundColor": "rgba(0, 255, 0, 0.25)",
+                "data": [6, 2, null, 4, 5, null, null, 2, 1]
+            }, {
+                "backgroundColor": "rgba(255, 0, 0, 0.25)",
+                "data": [7, 3, 4, 5, 6, 1, 4, null, null]
+            }, {
+                "backgroundColor": "rgba(0, 0, 255, 0.25)",
+                "data": [8, 7, 6, -6, -4, -6, 4, 5, 8]
+            }]
+        },
+        "options": {
+            "responsive": false,
+            "spanGaps": true,
+            "legend": false,
+            "title": false,
+            "scales": {
+                "xAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }],
+                "yAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }]
+            },
+            "elements": {
+                "point": {
+                    "radius": 0
+                },
+                "line": {
+                    "borderColor": "transparent",
+                    "fill": "bottom",
+                    "tension": 0
+                }
+            }
+        }
+    },
+    "options": {
+        "canvas": {
+            "height": 256,
+            "width": 512
+        }
+    }
+}

test/fixtures/element.line/fill-line-bottom.json

@@ -0,0 +1,55 @@
+{
+    "config": {
+        "type": "line",
+        "data": {
+            "labels": ["0", "1", "2", "3", "4", "5", "6", "7", "8"],
+            "datasets": [{
+                "backgroundColor": "rgba(0, 0, 255, 0.25)",
+                "data": [null, null, 2, 3, 4, -4, -2, 1, 0]
+            }, {
+                "backgroundColor": "rgba(0, 255, 0, 0.25)",
+                "data": [6, 2, null, 4, 5, null, null, 2, 1]
+            }, {
+                "backgroundColor": "rgba(255, 0, 0, 0.25)",
+                "data": [7, 3, 4, 5, 6, 1, 4, null, null]
+            }, {
+                "backgroundColor": "rgba(0, 0, 255, 0.25)",
+                "data": [8, 7, 6, -6, -4, -6, 4, 5, 8]
+            }]
+        },
+        "options": {
+            "responsive": false,
+            "spanGaps": false,
+            "legend": false,
+            "title": false,
+            "scales": {
+                "xAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }],
+                "yAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }]
+            },
+            "elements": {
+                "point": {
+                    "radius": 0
+                },
+                "line": {
+                    "borderColor": "transparent",
+                    "fill": "bottom",
+                    "tension": 0
+                }
+            }
+        }
+    },
+    "options": {
+        "canvas": {
+            "height": 256,
+            "width": 512
+        }
+    }
+}

test/fixtures/element.line/fill-line-spline-span.json

@@ -0,0 +1,55 @@
+{
+    "config": {
+        "type": "line",
+        "data": {
+            "labels": ["0", "1", "2", "3", "4", "5", "6", "7", "8"],
+            "datasets": [{
+                "backgroundColor": "rgba(0, 0, 192, 0.25)",
+                "data": [null, null, 2, 4, 2, 1, -1, 1, 2]
+            }, {
+                "backgroundColor": "rgba(0, 192, 0, 0.25)",
+                "data": [4, 2, null, 3, 2.5, null, -2, 1.5, 3]
+            }, {
+                "backgroundColor": "rgba(192, 0, 0, 0.25)",
+                "data": [3.5, 2, 1, 2.5, -2, 3, -1, null, null]
+            }, {
+                "backgroundColor": "rgba(128, 0, 128, 0.25)",
+                "data": [5, 6, 5, -2, -4, -3, 4, 2, 4.5]
+            }]
+        },
+        "options": {
+            "responsive": false,
+            "spanGaps": true,
+            "legend": false,
+            "title": false,
+            "scales": {
+                "xAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }],
+                "yAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }]
+            },
+            "elements": {
+                "point": {
+                    "radius": 0
+                },
+                "line": {
+                    "cubicInterpolationMode": "monotone",
+                    "borderColor": "transparent",
+                    "fill": "zero"
+                }
+            }
+        }
+    },
+    "options": {
+        "canvas": {
+            "height": 256,
+            "width": 512
+        }
+    }
+}

test/fixtures/element.line/fill-line-spline.json

@@ -0,0 +1,55 @@
+{
+    "config": {
+        "type": "line",
+        "data": {
+            "labels": ["0", "1", "2", "3", "4", "5", "6", "7", "8"],
+            "datasets": [{
+                "backgroundColor": "rgba(0, 0, 192, 0.25)",
+                "data": [null, null, 2, 4, 2, 1, -1, 1, 2]
+            }, {
+                "backgroundColor": "rgba(0, 192, 0, 0.25)",
+                "data": [4, 2, null, 3, 2.5, null, -2, 1.5, 3]
+            }, {
+                "backgroundColor": "rgba(192, 0, 0, 0.25)",
+                "data": [3.5, 2, 1, 2.5, -2, 3, -1, null, null]
+            }, {
+                "backgroundColor": "rgba(128, 0, 128, 0.25)",
+                "data": [5, 6, 5, -2, -4, -3, 4, 2, 4.5]
+            }]
+        },
+        "options": {
+            "responsive": false,
+            "spanGaps": false,
+            "legend": false,
+            "title": false,
+            "scales": {
+                "xAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }],
+                "yAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }]
+            },
+            "elements": {
+                "point": {
+                    "radius": 0
+                },
+                "line": {
+                    "cubicInterpolationMode": "monotone",
+                    "borderColor": "transparent",
+                    "fill": "zero"
+                }
+            }
+        }
+    },
+    "options": {
+        "canvas": {
+            "height": 256,
+            "width": 512
+        }
+    }
+}

test/fixtures/element.line/fill-line-stepped-span.json

@@ -0,0 +1,56 @@
+{
+    "config": {
+        "type": "line",
+        "data": {
+            "labels": ["0", "1", "2", "3", "4", "5", "6", "7", "8"],
+            "datasets": [{
+                "backgroundColor": "rgba(0, 0, 192, 0.25)",
+                "data": [null, null, 2, 4, 2, 1, -1, 1, 2]
+            }, {
+                "backgroundColor": "rgba(0, 192, 0, 0.25)",
+                "data": [4, 2, null, 3, 2.5, null, -2, 1.5, 3]
+            }, {
+                "backgroundColor": "rgba(192, 0, 0, 0.25)",
+                "data": [3.5, 2, 1, 2.5, -2, 3, -1, null, null]
+            }, {
+                "backgroundColor": "rgba(128, 0, 128, 0.25)",
+                "data": [5, 6, 5, -2, -4, -3, 4, 2, 4.5]
+            }]
+        },
+        "options": {
+            "responsive": false,
+            "spanGaps": true,
+            "legend": false,
+            "title": false,
+            "scales": {
+                "xAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }],
+                "yAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }]
+            },
+            "elements": {
+                "point": {
+                    "radius": 0
+                },
+                "line": {
+                    "cubicInterpolationMode": "monotone",
+                    "borderColor": "transparent",
+                    "stepped": true,
+                    "fill": "zero"
+                }
+            }
+        }
+    },
+    "options": {
+        "canvas": {
+            "height": 256,
+            "width": 512
+        }
+    }
+}

test/fixtures/element.line/fill-line-stepped.json

@@ -0,0 +1,56 @@
+{
+    "config": {
+        "type": "line",
+        "data": {
+            "labels": ["0", "1", "2", "3", "4", "5", "6", "7", "8"],
+            "datasets": [{
+                "backgroundColor": "rgba(0, 0, 192, 0.25)",
+                "data": [null, null, 2, 4, 2, 1, -1, 1, 2]
+            }, {
+                "backgroundColor": "rgba(0, 192, 0, 0.25)",
+                "data": [4, 2, null, 3, 2.5, null, -2, 1.5, 3]
+            }, {
+                "backgroundColor": "rgba(192, 0, 0, 0.25)",
+                "data": [3.5, 2, 1, 2.5, -2, 3, -1, null, null]
+            }, {
+                "backgroundColor": "rgba(128, 0, 128, 0.25)",
+                "data": [5, 6, 5, -2, -4, -3, 4, 2, 4.5]
+            }]
+        },
+        "options": {
+            "responsive": false,
+            "spanGaps": false,
+            "legend": false,
+            "title": false,
+            "scales": {
+                "xAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }],
+                "yAxes": [{
+                    "ticks": {
+                        "display": false
+                    }
+                }]
+            },
+            "elements": {
+                "point": {
+                    "radius": 0
+                },
+                "line": {
+                    "cubicInterpolationMode": "monotone",
+                    "borderColor": "transparent",
+                    "stepped": true,
+                    "fill": "zero"
+                }
+            }
+        }
+    },
+    "options": {
+        "canvas": {
+            "height": 256,
+            "width": 512
+        }
+    }
+}