Add tests for mixed number in KAS (#1507)

## Summary:

This is a failed attempt at [LEMS-2198](https://khanacademy.atlassian.net/browse/LEMS-2198), but I want to keep the tests to help the next person who tries.

[LEMS-2198]: https://khanacademy.atlassian.net/browse/LEMS-2198?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: handeyeco

Reviewers: SonicScrewdriver, mark-fitzgerald

Required Reviewers:

Approved By: SonicScrewdriver, mark-fitzgerald

Checks: ✅ codecov/project, ✅ codecov/patch, ✅ Upload Coverage (ubuntu-latest, 20.x), ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Check builds for changes in size (ubuntu-latest, 20.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ Jest Coverage (ubuntu-latest, 20.x), ✅ Cypress (ubuntu-latest, 20.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ gerald, ✅ Upload Coverage (ubuntu-latest, 20.x), ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Cypress (ubuntu-latest, 20.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ Jest Coverage (ubuntu-latest, 20.x), ✅ Check builds for changes in size (ubuntu-latest, 20.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ Publish Storybook to Chromatic (ubuntu-latest, 20.x), ✅ gerald

Pull Request URL: #1507

.changeset/gentle-dingos-explain.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/kas": patch
+---
+
+Add some tests for mixed numbers in KAS.

packages/kas/src/__tests__/evaluating.test.ts

@@ -13,11 +13,16 @@ expect.extend({
         vars: Variables = {},
         functions?: ReadonlyArray<string>,
     ) {
-        const actual = KAS.parse(input, {functions: functions}).expr.eval(
-            vars,
-            {functions: functions},
-        );
+        const parsed = KAS.parse(input, {functions: functions});
+        if (parsed.false || parsed.error) {
+            return {
+                pass: false,
+                message: () =>
+                    `unable to parse: ${input} (error: ${parsed.error})`,
+            };
+        }
 
+        const actual = parsed.expr.eval(vars, {functions: functions});
         if (actual !== expected) {
             return {
                 pass: false,
@@ -96,4 +101,40 @@ describe("evaluating", () => {
         expect("f(x-1)-f(x)").toEvaluateAs(-7, {f: "x^3", x: 2}, ["f"]);
         expect("g(1)").toEvaluateAs(-1, {f: "x", g: "-f(x)"}, ["f", "g"]);
     });
+
+    // TODO (LEMS-2198): these are tests from a failed attempt
+    // to support mixed numbers correctly. Keeping so we have a record
+    // of what's wrong and what's expected.
+    test("fraction expressions", () => {
+        // wrong
+        expect("2\\frac{1}{2} + 1").toEvaluateAs(2);
+        // correct
+        // expect("2\\frac{1}{2} + 1").toEvaluateAs(3.5);
+
+        // wrong
+        expect("(2\\frac{1}{2}) + 1").toEvaluateAs(2);
+        // correct
+        // expect("(2\\frac{1}{2}) + 1").toEvaluateAs(3.5);
+
+        // wrong
+        expect("-2\\frac{1}{2} + 1").toEvaluateAs(0);
+        // correct
+        // expect("-2\\frac{1}{2} + 1").toEvaluateAs(-1.5);
+
+        // wrong
+        expect("(-2\\frac{1}{2}) + 1").toEvaluateAs(0);
+        // correct
+        // expect("(-2\\frac{1}{2}) + 1").toEvaluateAs(-1.5);
+
+        // should continue to pass after LEMS-2198 is done
+        expect("2-\\frac{1}{2} + 1").toEvaluateAs(2.5);
+        expect("(2-\\frac{1}{2}) + 1").toEvaluateAs(2.5);
+        expect("(2)\\frac{1}{2} + 1").toEvaluateAs(2);
+        expect("2(\\frac{1}{2}) + 1").toEvaluateAs(2);
+        expect("\\frac{1}{2}2 + 1").toEvaluateAs(2);
+        expect("2 + \\frac{1}{2} + 1").toEvaluateAs(3.5);
+        expect("2 * \\frac{1}{2}").toEvaluateAs(1);
+        expect("2 2").toEvaluateAs(4);
+        expect("2\\pi").toEvaluateAs(6.283185307179586);
+    });
 });

packages/kas/src/__tests__/parsing.test.ts

@@ -13,7 +13,8 @@ expect.extend({
         if (actual !== expected) {
             return {
                 pass: false,
-                message: () => `${input} parses as ${expected}`,
+                message: () =>
+                    `input: ${input}\nexpected:${expected}\nactual: ${actual}`,
             };
         }
 
@@ -113,6 +114,8 @@ describe("parsing", () => {
         expect("\\frac{42}{1}").toParseAs("42/1");
         expect("\\frac{0}{42}").toParseAs("0/42");
 
+        // TODO (LEMS-2198): this should actually be:
+        // expect("2\\frac{1}{2}").toParseAs("2+1/2");
         expect("2\\frac{1}{2}").toParseAs("2*1/2");
         expect("\\frac{1}{2}\\frac{1}{2}").toParseAs("1/2*1/2");
         expect("-\\frac{1}{2}").toParseAs("-1/2");
@@ -128,6 +131,8 @@ describe("parsing", () => {
         expect("\\dfrac{42}{1}").toParseAs("42/1");
         expect("\\dfrac{0}{42}").toParseAs("0/42");
 
+        // TODO (LEMS-2198): this should actually be:
+        // expect("2\\dfrac{1}{2}").toParseAs("2+1/2");
         expect("2\\dfrac{1}{2}").toParseAs("2*1/2");
         expect("\\dfrac{1}{2}\\dfrac{1}{2}").toParseAs("1/2*1/2");
         expect("-\\dfrac{1}{2}").toParseAs("-1/2");