Enable configuration overrides via matcher

README.md

@@ -145,6 +145,25 @@ describe("My fancy image", () => {
 });
 ```
 
+It is possible to specify the image comparison configuration at the matcher level.
+Configuration set at this level will be merged into the main configuration, with keys
+defined at this level taking precedence.
+
+```typescript
+describe("My quite flaky image", () => {
+    const myFlakyImage = readFileSync("../my-flaky-image.png");
+
+    it("is a bit flaky", () => {
+        expect(myFlakyImage).toMatchImageSnapshot({
+           detectAntialiasing: true,
+           colorThreshold: 0.1,
+           pixelThresholdAbsolute: 25,
+           pixelThresholdRelative: 0.1
+        });
+    });
+});
+```
+
 It is possible to import ```toMatchImageSnapshot()``` for custom assertions.
 As it requires configuration as second argument, ```config()``` function 
 (_which is responsible for reading configuration from  jest-screenshot.json/package.json_) is also exposed.

src/__tests__/__snapshots__/test-to-match-image-snapshot.ts.snap

@@ -23,57 +23,86 @@ exports[`toMatchImageSnapshot when called outside of a jest unit test context fa
 
 exports[`toMatchImageSnapshot with \`.not\` specified fails always 1`] = `"Jest: \`.not\` cannot be used with \`.toMatchImageSnapshot()\`."`;
 
+exports[`toMatchImageSnapshot with a custom path provided fails with a non-matching screenshot 2`] = `
+"Received value does not match stored snapshot 1.
+
+Expected less than 0.00% of the pixels to have changed, but 45.44% of the pixels changed."
+`;
+
+exports[`toMatchImageSnapshot with a custom path provided fails with a non-matching screenshot and writes the report 2`] = `
+"Received value does not match stored snapshot 1.
+
+Expected less than 0.00% of the pixels to have changed, but 45.44% of the pixels changed."
+`;
+
 exports[`toMatchImageSnapshot with an absolute threshold provided fails with an absolute threshold of 204 2`] = `
 "Received value does not match stored snapshot 1.
 
 Expected less than 204 pixels to have changed, but 205 pixels changed."
 `;
 
+exports[`toMatchImageSnapshot with an absolute threshold provided fails with an absolute threshold of 204 passed through matcher params 2`] = `
+"Received value does not match stored snapshot 1.
+
+Expected less than 204 pixels to have changed, but 205 pixels changed."
+`;
+
 exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0 detects the snapshot as not matching 2`] = `
 "Received value does not match stored snapshot 1.
 
 Expected less than 0.00% of the pixels to have changed, but 53.24% of the pixels changed."
 `;
 
+exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0 provided through matcher params detects the snapshot as not matching 2`] = `
+"Received value does not match stored snapshot 1.
+
+Expected less than 0.00% of the pixels to have changed, but 53.24% of the pixels changed."
+`;
+
 exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0.1 detects the snapshot as not matching 2`] = `
 "Received value does not match stored snapshot 1.
 
 Expected less than 0.00% of the pixels to have changed, but 45.44% of the pixels changed."
 `;
 
+exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0.1 provided through matcher params detects the snapshot as not matching 2`] = `
+"Received value does not match stored snapshot 1.
+
+Expected less than 0.00% of the pixels to have changed, but 45.44% of the pixels changed."
+`;
+
 exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0.5 detects the snapshot as not matching 2`] = `
 "Received value does not match stored snapshot 1.
 
 Expected less than 0.00% of the pixels to have changed, but 12.52% of the pixels changed."
 `;
 
-exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0.6 detects the snapshot as not matching 2`] = `
+exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0.5 provided through matcher params detects the snapshot as not matching 2`] = `
 "Received value does not match stored snapshot 1.
 
-Expected less than 0.00% of the pixels to have changed, but 4.10% of the pixels changed."
+Expected less than 0.00% of the pixels to have changed, but 12.52% of the pixels changed."
 `;
 
-exports[`toMatchImageSnapshot with the snapshot not existing fails when updating is disabled 2`] = `
-"New snapshot was not written. The update flag must be explicitly passed to write a new snapshot.
+exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0.6 detects the snapshot as not matching 2`] = `
+"Received value does not match stored snapshot 1.
 
-This is likely because this test is run in a continuous integration (CI) environment in which snapshots are not written by default."
+Expected less than 0.00% of the pixels to have changed, but 4.10% of the pixels changed."
 `;
 
-exports[`toMatchImageSnapshot with the snapshot not matching fails when updating is disabled 2`] = `
+exports[`toMatchImageSnapshot with no threshold provided with a color threshold of 0.6 provided through matcher params detects the snapshot as not matching 2`] = `
 "Received value does not match stored snapshot 1.
 
-Expected less than 0.00% of the pixels to have changed, but 45.44% of the pixels changed."
+Expected less than 0.00% of the pixels to have changed, but 4.10% of the pixels changed."
 `;
 
-exports[`toMatchImageSnapshot with a custom path provided fails with a non-matching screenshot 2`] = `
-"Received value does not match stored snapshot 1.
+exports[`toMatchImageSnapshot with the snapshot not existing fails when updating is disabled 2`] = `
+"New snapshot was not written. The update flag must be explicitly passed to write a new snapshot.
 
-Expected less than 0.00% of the pixels to have changed, but 45.44% of the pixels changed."
+This is likely because this test is run in a continuous integration (CI) environment in which snapshots are not written by default."
 `;
 
-exports[`toMatchImageSnapshot with a custom path provided fails with a non-matching screenshot and writes the report 2`] = `
+exports[`toMatchImageSnapshot with the snapshot not matching fails when updating is disabled 2`] = `
 "Received value does not match stored snapshot 1.
 
 Expected less than 0.00% of the pixels to have changed, but 45.44% of the pixels changed."
 `;
-

src/__tests__/test-to-match-image-snapshot.ts

@@ -61,6 +61,15 @@ describe("toMatchImageSnapshot", () => {
                     expect(readFileSync(`${__dirname}/fixtures/red-rectangle-example-red.png`)).toMatchImageSnapshot();
                 }).toThrowErrorMatchingSnapshot();
             });
+
+            it(`with a color threshold of ${colorThreshold} provided through matcher params detects the snapshot as not matching`, () => {
+                writeFileSync(`${process.cwd()}/jest-screenshot.json`, JSON.stringify({}));
+                setupJestScreenshot();
+                expect(() => {
+                    expect(readFileSync(`${__dirname}/fixtures/red-rectangle-example-red.png`))
+                      .toMatchImageSnapshot({colorThreshold});
+                }).toThrowErrorMatchingSnapshot();
+            });
         });
 
         [
@@ -74,6 +83,15 @@ describe("toMatchImageSnapshot", () => {
                     expect(readFileSync(`${__dirname}/fixtures/red-rectangle-example-red.png`)).toMatchImageSnapshot();
                 }).not.toThrowError();
             });
+
+            it(`with a color threshold of ${colorThreshold} provided through matcher params detects the snapshot as matching`, () => {
+                writeFileSync(`${process.cwd()}/jest-screenshot.json`, JSON.stringify({  }));
+                setupJestScreenshot();
+                expect(() => {
+                    expect(readFileSync(`${__dirname}/fixtures/red-rectangle-example-red.png`))
+                      .toMatchImageSnapshot({colorThreshold});
+                }).not.toThrowError();
+            });
         });
     });
 
@@ -92,6 +110,18 @@ describe("toMatchImageSnapshot", () => {
             }).toThrowErrorMatchingSnapshot();
         });
 
+        it("fails with an absolute threshold of 204 passed through matcher params", () => {
+            const pixelThresholdAbsolute = 204;
+            writeFileSync(`${process.cwd()}/jest-screenshot.json`, JSON.stringify({
+                colorThreshold,
+            }));
+            setupJestScreenshot();
+            expect(() => {
+                expect(readFileSync(`${__dirname}/fixtures/red-rectangle-example-red.png`))
+                  .toMatchImageSnapshot({pixelThresholdAbsolute});
+            }).toThrowErrorMatchingSnapshot();
+        });
+
         it("passes with an absolute threshold of 205", () => {
             const pixelThresholdAbsolute = 205;
             writeFileSync(`${process.cwd()}/jest-screenshot.json`, JSON.stringify({
@@ -103,6 +133,20 @@ describe("toMatchImageSnapshot", () => {
                 expect(readFileSync(`${__dirname}/fixtures/red-rectangle-example-red.png`)).toMatchImageSnapshot();
             }).not.toThrowError();
         });
+
+        it("passes with an absolute threshold of 205 passed through matcher params", () => {
+            const pixelThresholdAbsolute = 205;
+            writeFileSync(`${process.cwd()}/jest-screenshot.json`, JSON.stringify({
+                colorThreshold,
+            }));
+            setupJestScreenshot();
+            expect(() => {
+                expect(readFileSync(`${__dirname}/fixtures/red-rectangle-example-red.png`))
+                  .toMatchImageSnapshot({
+                      pixelThresholdAbsolute,
+                  });
+            }).not.toThrowError();
+        });
     });
 
     describe("with `.not` specified", () => {

src/config.ts

@@ -65,10 +65,10 @@ function getPackageConfig() {
     }
 }
 
-export function config(customConfig?: JestScreenshotConfiguration): JestScreenshotConfiguration {
+export function config(...customConfigs: JestScreenshotConfiguration[]): JestScreenshotConfiguration {
     const fileConfig = getFileConfig();
     const packageConfig = getPackageConfig();
-    const configuration = Object.assign({}, packageConfig, fileConfig, customConfig);
+    const configuration = Object.assign({}, packageConfig, fileConfig, ...customConfigs);
     const { pixelThresholdAbsolute, pixelThresholdRelative } = configuration;
     if (typeof pixelThresholdAbsolute === "undefined" && typeof pixelThresholdRelative === "undefined") {
         configuration.pixelThresholdRelative = 0;

src/jest-screenshot.ts

@@ -13,7 +13,7 @@ export function setupJestScreenshot(customConfig?: JestScreenshotConfiguration)
     }
     expect.extend({
         toMatchImageSnapshot(received: Buffer, parameters: ToMatchImageSnapshotParameters) {
-            return toMatchImageSnapshot.call(this, received, config(customConfig), parameters);
+            return toMatchImageSnapshot.call(this, received, config(customConfig, parameters), parameters);
         },
     });
 }

src/to-match-image-snapshot.ts

@@ -17,7 +17,14 @@ export interface ImageMatcherResult extends MatcherResult {
     snapshotNumber?: number;
 }
 
-export interface ToMatchImageSnapshotParameters {
+export interface ToMatchImageSnapshotParameters extends
+    Pick<
+        JestScreenshotConfiguration,
+        | "detectAntialiasing"
+        | "colorThreshold"
+        | "pixelThresholdAbsolute"
+        | "pixelThresholdRelative"
+    > {
     /**
      * Can be used to override the path to which the snapshot image
      * will be written.