Add coverage Istanbul Reporter to karma configuration

frontend/karma.conf.js

@@ -31,12 +31,66 @@ module.exports = (config) => {
             "tests/unit/**/*_test.js": ["webpack"],
         },
 
-        reporters: ["progress", "html"],
+        reporters: ["progress", "html", "coverage-istanbul"],
 
         htmlReporter: {
             outputFile: "tests/unit.html",
         },
 
+        coverageIstanbulReporter: {
+            // reports can be any that are listed here: https://github.com/istanbuljs/istanbuljs/tree/aae256fb8b9a3d19414dcf069c592e88712c32c6/packages/istanbul-reports/lib
+            reports: ["html", "lcovonly", "text-summary"],
+
+            // base output directory. If you include %browser% in the path it will be replaced with the karma browser name
+            dir: path.join(__dirname, "coverage"),
+
+            // Combines coverage information from multiple browsers into one report rather than outputting a report
+            // for each browser.
+            combineBrowserReports: true,
+
+            // if using webpack and pre-loaders, work around webpack breaking the source path
+            fixWebpackSourcePaths: true,
+
+            // Omit files with no statements, no functions and no branches from the report
+            skipFilesWithNoCoverage: true,
+
+            // Most reporters accept additional config options. You can pass these through the `report-config` option
+            "report-config": {
+                // all options available at: https://github.com/istanbuljs/istanbuljs/blob/aae256fb8b9a3d19414dcf069c592e88712c32c6/packages/istanbul-reports/lib/html/index.js#L135-L137
+                html: {
+                    // outputs the report in ./coverage/html
+                    subdir: "html",
+                },
+            },
+
+            // enforce percentage thresholds
+            // anything under these percentages will cause karma to fail with an exit code of 1 if not running in watch mode
+            thresholds: {
+                emitWarning: true, // set to `true` to not fail the test command when thresholds are not met
+                // thresholds for all files
+                global: {
+                    statements: 100,
+                    lines: 100,
+                    branches: 100,
+                    functions: 100,
+                },
+                // thresholds per file
+                each: {
+                    statements: 100,
+                    lines: 100,
+                    branches: 100,
+                    functions: 100,
+                    overrides: {
+                        "baz/component/**/*.js": {
+                            statements: 98,
+                        },
+                    },
+                },
+            },
+
+            verbose: false, // output config used by istanbul for debugging
+        },
+
         webpack: {
             mode: "development",