1 files changed, 71 insertions, 0 deletions
diff --git a/devtools/client/inspector/fonts/test/browser_fontinspector_editor-letter-spacing-conversion.js b/devtools/client/inspector/fonts/test/browser_fontinspector_editor-letter-spacing-conversion.js
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index 0000000000..ff680717a9
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+++ b/devtools/client/inspector/fonts/test/browser_fontinspector_editor-letter-spacing-conversion.js
@@ -0,0 +1,71 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+/* global getPropertyValue */
+
+"use strict";
+
+// Unit test for math behind conversion of units for letter-spacing.
+
+const TEST_URI = `
+  <style type='text/css'>
+    body {
+      /* Set root font-size to equivalent of 32px (2*16px) */
+      font-size: 200%;
+    }
+    div {
+      letter-spacing: 1em;
+    }
+  </style>
+  <div>LETTER SPACING</div>
+`;
+
+add_task(async function () {
+  const URI = "data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI);
+  const { inspector, view } = await openFontInspectorForURL(URI);
+  const viewDoc = view.document;
+  const property = "letter-spacing";
+  const UNITS = {
+    px: 32,
+    rem: 2,
+    em: 1,
+  };
+
+  await selectNode("div", inspector);
+
+  info("Check that font editor shows letter-spacing value in original units");
+  const letterSpacing = getPropertyValue(viewDoc, property);
+  is(
+    letterSpacing.value + letterSpacing.unit,
+    "1em",
+    "Original letter spacing is 1em"
+  );
+
+  // Starting value and unit for conversion.
+  let prevValue = letterSpacing.value;
+  let prevUnit = letterSpacing.unit;
+
+  for (const unit in UNITS) {
+    const value = UNITS[unit];
+
+    info(`Convert letter-spacing from ${prevValue}${prevUnit} to ${unit}`);
+    const convertedValue = await view.convertUnits(
+      property,
+      prevValue,
+      prevUnit,
+      unit
+    );
+    is(
+      convertedValue,
+      value,
+      `Converting to ${unit} returns transformed value.`
+    );
+
+    // Store current unit and value to use in conversion on the next iteration.
+    prevUnit = unit;
+    prevValue = value;
+  }
+
+  info(`Check that conversion to fake unit returns 1-to-1 mapping`);
+  const valueToFakeUnit = await view.convertUnits(property, 1, "px", "fake");
+  is(valueToFakeUnit, 1, `Converting to fake unit returns same value.`);
+});